N-CSRS

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED MANAGEMENT

INVESTMENT COMPANIES

Investment Company Act file number 811-5360

Oppenheimer Main Street Funds

(Exact name of registrant as specified in charter)

6803 South Tucson Way, Centennial, Colorado 80112-3924

(Address of principal executive offices) (Zip code)

Cynthia Lo Bessette

OFI Global Asset Management, Inc.

225 Liberty Street, New York, New York 10281-1008

(Name and address of agent for service)

Registrant’s telephone number, including area code: (303) 768-3200

Date of fiscal year end: August 31

Date of reporting period: 2/28/2018

Item 1. Reports to Stockholders.

Semiannual Report	2/28/2018
OppenheimerFunds® The Right Way to Invest

Table of Contents

Fund Performance Discussion	3
Top Holdings and Allocations	6
Fund Expenses	9
Statement of Investments	11
Statement of Assets and Liabilities	14
Statement of Operations	16
Statements of Changes in Net Assets	17
Financial Highlights	18
Notes to Financial Statements	30
Portfolio Proxy Voting Policies and Guidelines; Updates to Statement of Investments	43
Distribution Sources	44
Trustees and Officers	45
Privacy Notice	46

Class A Shares

AVERAGE ANNUAL TOTAL RETURNS AT 2/28/18

	Class A Shares of the Fund
	Without Sales Charge			With Sales Charge			S&P 500 Index
6-Month		3.98	%		-2.00	%		10.84	%
1-Year		10.25			3.91			17.10
5-Year		13.24			11.91			14.73
10-Year		8.68			8.03			9.73

Performance data quoted represents past performance, which does not guarantee future results. The investment return and principal value of an investment in the Fund will fluctuate so that an investor’s shares, when redeemed, may be worth more or less than their original cost. Fund returns include changes in share price, reinvested distributions, and a 5.75% maximum applicable sales charge except where “without sales charge” is indicated. Current performance may be lower or higher than the performance quoted. Returns do not consider capital gains or income taxes on an individual’s investment. Returns for periods of less than one year are cumulative and not annualized. For performance data current to the most recent month-end, visit oppenheimerfunds.com or call 1.800.CALL OPP (225.5677). See Fund prospectuses and summary prospectuses for more information on share classes and sales charges.

2      OPPENHEIMER MAIN STREET FUND

Fund Performance Discussion

The Fund’s Class A shares (without sales charge) returned 3.98% during the six-month reporting period. In comparison, the Fund underperformed the S&P 500 Index (the “Index”), which returned 10.84%, primarily due to less favorable stock selection in the Industrials, Consumer Discretionary, and Health Care sectors. Relative to the Index, positive contributors for the Fund were Financials and Real Estate, where an overweight and underweight position contributed to performance, respectively.

MARKET OVERVIEW

2017 was a banner year in terms of fundamentals for the U.S. economy and that enthusiasm bled into January 2018. The market hit a speed bump in February as inflation showed signs of accelerating and volatility spiked higher after a sustained period of being at historically low levels. We are watching bond yields and spreads carefully and expect heightened volatility to remain throughout the year. That said, we believe corporate tax reform will increase earnings and cash flow for most companies and likely boost economic growth in the short-term. In general, valuation has taken a back-seat in the current market environment as investors have favored disruptive companies as well as growth-style investments over the value style.

As investors, it is important to know what is and what is not within one’s circle of competence. As such, we strive to keep the portfolio in an all-weather orientation. Whether rates, commodity prices, currencies or even whole economies go up or down, we seek to have a portfolio that can outperform no matter the environment, although we do have a history of underperforming in

go-go markets (like 2017) and outperforming in down markets.

If our strategy includes not making oversized macro factor bets, a reasonable question is, “What types of risks are you willing to take?” First, we believe identifying companies with sustainable competitive advantages (or economic moats, if you prefer), is squarely in the middle of our circle of competence.

Second, we believe we have the skills to identify company management teams that are likely to successfully execute on their plans. Lastly, we believe that correctly valuing stocks and seeing what expectations the market is pricing in is also within our skillset. It is not by accident that we typically weight the portfolio more heavily towards companies that have structural competitive advantages and/or management teams that are executing (e.g., gaining market share, expanding profit margins), with at least reasonable stock valuations. Companies with these qualities generally have more stable earnings.

3      OPPENHEIMER MAIN STREET FUND

Allow us to use a metaphor. If managing the portfolio was like betting on horses, we’d readily admit that we cannot predict ahead of time the weather or track conditions. But we do believe we can find the strongest horses (advantaged business models), the best jockeys (executing management teams), and can see when the payoff odds are in our favor (positive expected returns). To offset our agnostic position on the conditions, we try to have some horses in the stable that will win no matter the weather. In short, it boils down to mostly stock selection. This approach has led to consistent positive alpha versus our peers over longer periods of time.

FUND REVIEW

Top contributing holdings to performance this reporting period included CME Group, AutoZone, and Progressive. CME Group had a strong February 2018 as the month witnessed increased volatility in the markets, which caused the contracts traded on the CME to spike to record levels. In addition, open interest, which is a barometer for backlog and future trading volumes on the exchange, hit 132 million contracts, well above all prior records at the company. After underperforming for most of 2017, AutoZone sharply rebounded in November 2017. The prior underperformance was driven by a deceleration in same store sales and the narrative that the deceleration was partially being driven by Amazon encroaching on the auto parts retail business. The stock rebounded after a stabilization of same store sales and lessening concerns about the health of the industry. Progressive continued to beat consensus earnings expectations, driven by market share gains in

auto insurance, better pricing (higher premiums), and lower than expected auto claims. In January 2018, Progressive was negatively impacted by the general underperformance of the Insurance sub-sector within Financials after being a strong performer during the fourth quarter of 2017. In addition, there were some concerns that regulators would force auto insurers to pass along any benefits from recent U.S. corporate tax cuts along to their policy holders. However, the company bounced back in February strongly after this concern began to dissipate as the company continued to post better than expected monthly earnings.

Detractors from performance this reporting period included PG&E, Celgene, and Amazon. com. PG&E is one of the largest utility companies in California. The stock has been under pressure since the start of the Northern California wildfires due to concerns that some of the company’s equipment may have played a role in some of the fires. The stock saw further pressure after the company announced it would be suspending the dividend to preserve cash for potential future claims. Celgene experienced significant weakness in October 2017 after lowering earnings guidance for 2017 and longer term through 2020. This was primarily due to lower expected revenues from Otezla, a drug treating certain types of arthritis, which accounts for ~10% of the company’s revenues. Secondarily, there was disappointment due to the withdrawal of a pipeline drug. We have maintained our position as the stock price declined in-line with lowered conviction. Not owning Amazon detracted from performance as the company continued its run of impressive

4      OPPENHEIMER MAIN STREET FUND

performance and is one of largest names in the S&P 500 Index.

STRATEGY & OUTLOOK

As of period end, the U.S. economy continues its “slow and steady” growth. This is being driven by favorable data around employment, wages and inflation. Rising home prices and innovation have also continued to help drive the economy higher. Moreover, we believe corporate tax reform will lead to a jump in earnings and cash flow for most companies, and it will more likely than not lead to a boost in economic growth in the short term. While the economic expansionary cycle is indeed long in the tooth, the economic growth has been at relatively low rates, suggesting it could continue for a while longer.

We are afraid companies are addicted to low interest rates, which have been low for almost a decade now. We believe the risks inherent to this market include the misallocation of capital if interest rates were to rise materially. As the markets have risen, we find fewer companies with attractive fundamentals that are attractively

priced. We intend to maintain our discipline around valuation. Additionally, while innovation is alive and well and continuing to help generate economic growth, fundamental disruptions across market segments have been elevated. We continue to be focused on potential disruption risk to our companies.

Volatility in the markets was unusually low in 2017 and has returned to the equity markets as we expected it would. Traditionally, during periods of economic uncertainty and heightened market volatility, investors favor stocks of higher quality companies—with greater consistency and stability of revenue and earnings—leading to relatively better stock performance of those companies. We think focusing on companies with economic moats and skilled management teams positions us well, should this environment come to pass. During times of economic volatility such companies frequently widen their lead over weaker competitors. We seek to invest in companies, characterized by these qualities, at compelling valuations and believe this disciplined approach is essential to generating superior long-term performance.

Manind Govil, CFA Portfolio Manager

  Paul Larson Portfolio Manager

Benjamin Ram Portfolio Manager

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Top Holdings and Allocations

TOP TEN COMMON STOCK HOLDINGS

Apple, Inc.	6.1%
Alphabet, Inc., Cl. C	5.0
JPMorgan Chase & Co.	3.3
Facebook, Inc., Cl. A	3.0
PepsiCo, Inc.	2.9
UnitedHealth Group, Inc.	2.8
Comcast Corp., Cl. A	2.6
Berkshire Hathaway, Inc., Cl. B	2.3
Merck & Co., Inc.	2.3
Lockheed Martin Corp.	2.3

Portfolio holdings and allocations are subject to change. Percentages are as of February 28, 2018, and are based on net assets. For more current Fund holdings, please visit oppenheimerfunds.com.

SECTOR ALLOCATION

TOP TEN COMMON STOCK INDUSTRIES

Internet Software & Services	9.3%
Technology Hardware, Storage & Peripherals	7.0
Capital Markets	6.7
Commercial Banks	5.9
Oil, Gas & Consumable Fuels	5.3
Specialty Retail	5.1
Health Care Providers & Services	4.9
Insurance	3.1
Biotechnology	3.0
Communications Equipment	2.9

Portfolio holdings and allocations are subject to change. Percentages are as of February 28, 2018, and are based on net assets.

Portfolio holdings and allocations are subject to change. Percentages are as of February 28, 2018, and are based on the total market value of common stocks.

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Share Class Performance

AVERAGE ANNUAL TOTAL RETURNS WITHOUT SALES CHARGE AS OF 2/28/18

	Inception Date		6-Month			1-Year			5-Year			10-Year
Class A (MSIGX)		2/3/88		3.98	%		10.25	%		13.24	%		8.68%
Class B (OMSBX)		10/3/94		3.58			9.40			12.35			8.12
Class C (MIGCX)		12/1/93		3.59			9.40			12.39			7.86
Class I (OMSIX)		12/29/11		4.19			10.69			13.72			14.60*
Class R (OMGNX)		3/1/01		3.82			9.95			12.95			8.39
Class Y (MIGYX)		11/1/96		4.09			10.49			13.52			9.06
AVERAGE ANNUAL TOTAL RETURNS WITH SALES CHARGE AS OF 2/28/18
	Inception Date		6-Month			1-Year			5-Year			10-Year
Class A (MSIGX)		2/3/88		-2.00	%		3.91	%		11.91	%		8.03%
Class B (OMSBX)		10/3/94		-1.28			4.40			12.10			8.12
Class C (MIGCX)		12/1/93		2.62			8.40			12.39			7.86
Class I (OMSIX)		12/29/11		4.19			10.69			13.72			14.60*
Class R (OMGNX)		3/1/01		3.82			9.95			12.95			8.39
Class Y (MIGYX)		11/1/96		4.09			10.49			13.52			9.06

*Shows performance since inception.

Performance data quoted represents past performance, which does not guarantee future results. The investment return and principal value of an investment in the Fund will fluctuate so that an investor’s shares, when redeemed, may be worth more or less than their original cost. Current performance may be lower or higher than the performance quoted. Returns do not consider capital gains or income taxes on an individual’s investment. For performance data current to the most recent month-end, visit oppenheimerfunds.com or call 1.800. CALL OPP (225.5677). Fund returns include changes in share price, reinvested distributions, and the applicable sales charge: for Class A shares, the current maximum initial sales charge of 5.75%; for Class B shares, the contingent deferred sales charge of 5% (1-year) and 2% (5-year); and for Class C shares, the contingent deferred sales charge of 1% for the 1-year period. There is no sales charge for Class I, Class R and Class Y shares. Because Class B shares convert to Class A shares 72 months after purchase, the 10-year return for Class B shares uses Class A performance for the period after conversion. Returns for periods of less than one year are cumulative and not annualized. See Fund prospectuses and summary prospectuses for more information on share classes and sales charges.

The Fund’s performance is compared to the performance of the S&P 500 Index. The S&P 500 Index is a capitalization-weighted index of 500 stocks intended to be a representative sample of leading companies in leading industries within the U.S. economy. The Index is unmanaged and cannot be purchased directly by investors. While index comparisons may be useful to provide a benchmark for the Fund’s performance, it must be noted that the Fund’s investments are not limited to the investments comprising the Index. Index performance includes reinvestment of income, but does not reflect transaction costs, fees, expenses or

7      OPPENHEIMER MAIN STREET FUND

taxes. Index performance is shown for illustrative purposes only as a benchmark for the Fund’s performance, and does not predict or depict performance of the Fund. The Fund’s performance reflects the effects of the Fund’s business and operating expenses.

The views in the Fund Performance Discussion represent the opinions of this Fund’s portfolio managers and are not intended as investment advice or to predict or depict the performance of any investment. These views are as of the close of business on February 28, 2018, and are subject to change based on subsequent developments. The Fund’s portfolio and strategies are subject to change.

Before investing in any of the Oppenheimer funds, investors should carefully consider a fund’s investment objectives, risks, charges and expenses. Fund prospectuses and summary prospectuses contain this and other information about the funds, and may be obtained by asking your financial advisor, visiting oppenheimerfunds.com, or calling 1.800.CALL OPP (225.5677). Read prospectuses and summary prospectuses carefully before investing.

Shares of Oppenheimer funds are not deposits or obligations of any bank, are not guaranteed by any bank, are not insured by the FDIC or any other agency, and involve investment risks, including the possible loss of the principal amount invested.

8      OPPENHEIMER MAIN STREET FUND

Fund Expenses

Fund Expenses. As a shareholder of the Fund, you incur two types of costs: (1) transaction costs, which may include sales charges (loads) on purchase payments and/or contingent deferred sales charges on redemptions; and (2) ongoing costs, including management fees; distribution and service fees; and other Fund expenses. These examples are intended to help you understand your ongoing costs (in dollars) of investing in the Fund and to compare these costs with the ongoing costs of investing in other mutual funds.

The examples are based on an investment of $1,000.00 invested at the beginning of the period and held for the entire 6-month period ended February 28, 2018.

Actual Expenses. The first section of the table provides information about actual account values and actual expenses. You may use the information in this section for the class of shares you hold, together with the amount you invested, to estimate the expense that you paid over the period. Simply divide your account value by $1,000.00 (for example, an $8,600.00 account value divided by $1,000.00 = 8.60), then multiply the result by the number in the first section under the heading entitled “Expenses Paid During 6 Months Ended February 28, 2018” to estimate the expenses you paid on your account during this period.

Hypothetical Example for Comparison Purposes. The second section of the table provides information about hypothetical account values and hypothetical expenses based on the Fund’s actual expense ratio for each class of shares, and an assumed rate of return of 5% per year for each class before expenses, which is not the Fund’s actual return. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period. You may use this information to compare the ongoing costs of investing in the Fund and other funds. To do so, compare this 5% hypothetical example for the class of shares you hold with the 5% hypothetical examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown in the table are meant to highlight your ongoing costs only and do not reflect any transactional costs, such as front-end or contingent deferred sales charges (loads). Therefore, the “hypothetical” section of the table is useful in comparing ongoing costs only, and will not help you determine the relative total costs of owning different funds. In addition, if these transactional costs were included, your costs would have been higher.

9      OPPENHEIMER MAIN STREET FUND

Actual	Beginning Account Value September 1, 2017		Ending Account Value February 28, 2018		Expenses Paid During 6 Months Ended February 28, 2018
Class A		$    1,000.00	$	1,039.80		$        4.56
Class B		1,000.00		1,035.80		8.51
Class C		1,000.00		1,035.90		8.41
Class I		1,000.00		1,041.90		2.53
Class R		1,000.00		1,038.20		5.88
Class Y		1,000.00		1,040.90		3.40
Hypothetical (5% return before expenses)
Class A		1,000.00		1,020.33		4.52
Class B		1,000.00		1,016.46		8.43
Class C		1,000.00		1,016.56		8.33
Class I		1,000.00		1,022.32		2.51
Class R		1,000.00		1,019.04		5.82
Class Y		1,000.00		1,021.47		3.36

Expenses are equal to the Fund’s annualized expense ratio for that class, multiplied by the average account value over the period, multiplied by 181/365 (to reflect the one-half year period). Those annualized expense ratios, excluding indirect expenses from affiliated funds, based on the 6-month period ended February 28, 2018 are as follows:

Class	Expense Ratios
Class A		0.90%
Class B		1.68
Class C		1.66
Class I		0.50
Class R		1.16
Class Y		0.67

The expense ratios reflect voluntary and/or contractual waivers and/or reimbursements of expenses by the Fund’s Manager and Transfer Agent. Some of these undertakings may be modified or terminated at any time, as indicated in the Fund’s prospectus. The “Financial Highlights” tables in the Fund’s financial statements, included in this report, also show the gross expense ratios, without such waivers or reimbursements and reduction to custodian expenses, if applicable.

10      OPPENHEIMER MAIN STREET FUND

STATEMENT OF INVESTMENTS February 28, 2018 Unaudited

	Shares		Value
Common Stocks—98.5%
Consumer Discretionary—10.8%
Auto Components—0.9%
Aptiv plc		869,762	$	79,435,364
Delphi Technologies plc		289,920		13,843,680
				93,279,044
Hotels, Restaurants & Leisure—1.8%
McDonald’s Corp.		1,136,810		179,320,409
Household Durables—0.4%
Whirlpool Corp.		269,700		43,807,371
Media—2.6%
Comcast Corp., Cl. A		7,153,028		259,011,144
Specialty Retail—5.1%
Best Buy Co., Inc.		779,020		56,432,209
CarMax, Inc.1		1,745,780		108,098,697
Lowe’s Cos., Inc.		2,089,740		187,219,807
O’Reilly Automotive, Inc.1		644,220		157,312,082
				509,062,795
Consumer Staples—7.5%
Beverages—2.9%
PepsiCo, Inc.		2,596,972		284,965,737
Food Products—2.8%
Kraft Heinz Co. (The)		2,128,340		142,705,197
Mondelez International, Inc., Cl. A		3,120,330		136,982,487
				279,687,684
Tobacco—1.8%
Philip Morris
International, Inc.		1,750,898		181,305,488
Energy—5.3%
Oil, Gas & Consumable Fuels—5.3%
Exxon Mobil Corp.		1,965,890		148,896,508
Magellan Midstream Partners LP2		2,758,643		172,304,842
Suncor Energy, Inc.		6,219,630		204,750,220
				525,951,570
Financials—19.8%
Capital Markets—6.7%
Bank of New York Mellon Corp. (The)		3,009,050		171,606,122

	Shares		Value
Capital Markets (Continued)
CME Group, Inc., Cl. A		989,430	$	164,403,689
Intercontinental Exchange, Inc.		2,236,680		163,456,574
S&P Global, Inc.		887,228		170,170,330
				669,636,715
Commercial Banks—5.9%
JPMorgan Chase & Co.		2,845,520		328,657,560
SunTrust Banks, Inc.		1,773,131		123,835,469
US Bancorp		2,599,650		141,316,974
				593,810,003
Consumer Finance—1.2%
Discover Financial Services		1,539,595		121,366,274
Diversified Financial Services—2.3%
Berkshire Hathaway, Inc., Cl. B1		1,132,710		234,697,512
Insurance—3.1%
Marsh & McLennan Cos., Inc.		1,774,000		147,277,480
Progressive Corp. (The)		2,737,770		157,640,796
				304,918,276
Real Estate Investment Trusts (REITs)—0.6%
Mid-America Apartment Communities, Inc.		727,713		62,452,330
Health Care—14.0%
Biotechnology—3.0%
Celgene Corp.1		1,473,036		128,330,896
Exact Sciences Corp.1		1,179,870		52,634,001
Gilead Sciences, Inc.		1,582,770		124,611,482
				305,576,379
Health Care Equipment & Supplies—2.1%
Boston Scientific Corp.1		3,359,900		91,590,874
Stryker Corp.		710,230		115,170,897
				206,761,771
Health Care Providers & Services—4.9%
DaVita, Inc.1		1,313,090		94,568,742
Express Scripts Holding Co.1		1,540,462		116,227,858

11      OPPENHEIMER MAIN STREET FUND

STATEMENT OF INVESTMENTS Unaudited / Continued

	Shares		Value
Health Care Providers & Services (Continued)
UnitedHealth Group, Inc.		1,235,787	$	279,485,588
				490,282,188
Health Care Technology—0.7%
Cerner Corp.1		1,104,650		70,874,344
Life Sciences Tools & Services—0.8%
Agilent Technologies, Inc.		1,233,400		84,598,906
Pharmaceuticals—2.5%
Merck & Co., Inc.		4,261,060		231,034,673
Valeant Pharmaceuticals International, Inc.1		1,055,120		17,293,417
				248,328,090
Industrials—9.3%
Aerospace & Defense—2.3%
Lockheed Martin Corp.		639,551		225,403,355
Airlines—0.5%
Alaska Air Group, Inc.		817,190		52,708,755
Commercial Services & Supplies—0.7%
Republic Services, Inc., Cl. A		1,083,040		72,758,627
Industrial Conglomerates—1.0%
General Electric Co.		7,158,180		101,001,920
Machinery—0.7%
Illinois Tool Works, Inc.		454,160		73,319,590
Professional Services—1.3%
Equifax, Inc.		413,920		46,772,960
Nielsen Holdings plc		2,630,265		85,825,547
				132,598,507
Road & Rail—1.9%
Canadian National Railway Co.		1,516,610		117,340,115
Canadian Pacific Railway Ltd.		407,817		72,848,351
				190,188,466
Trading Companies & Distributors—0.9%
Fastenal Co.		1,600,760		87,593,587
Information Technology—25.2%
Communications Equipment—2.9%
Cisco Systems, Inc.		2,050,280		91,811,538

	Shares		Value
Communications Equipment (Continued)
Motorola Solutions, Inc.		1,883,500	$	199,933,525
				291,745,063
Internet Software & Services—9.3%
Alphabet, Inc., Cl. C1		455,246		502,923,914
eBay, Inc.1		3,092,590		132,548,407
Facebook, Inc., Cl. A1		1,659,010		295,834,663
				931,306,984
IT Services—2.8%
Amdocs Ltd.		2,017,823		132,752,575
PayPal Holdings, Inc.1		1,851,790		147,050,644
				279,803,219
Semiconductors & Semiconductor Equipment—2.1%
Applied Materials, Inc.		2,622,860		151,050,507
Maxim Integrated Products, Inc.		1,061,220		64,670,747
				215,721,254
Software—1.1%
Activision Blizzard, Inc.		1,459,250		106,714,953
Technology Hardware, Storage & Peripherals—7.0%
Apple, Inc.		3,409,475		607,295,687
Western Digital Corp.		1,047,650		91,187,456
				698,483,143
Materials—2.9%
Chemicals—2.2%
DowDuPont, Inc.		1,483,325		104,277,748
PPG Industries, Inc.		1,074,580		120,825,775
				225,103,523
Construction Materials—0.7%
Vulcan Materials Co.		580,473		68,339,086
Telecommunication Services—1.3%
Diversified Telecommunication Services—1.3%
Verizon Communications, Inc.		2,731,420		130,397,991

12      OPPENHEIMER MAIN STREET FUND

	Shares			Value
Utilities—2.4%
Electric Utilities—1.0%
PG&E Corp.		2,300,360		$	94,521,792
Multi-Utilities—1.4%
National Grid plc		14,230,724			144,396,162
Total Common Stocks
(Cost $7,236,335,555)					9,871,800,007
Investment Company—1.9%
Oppenheimer Institutional Government Money Market Fund, Cl. E, 1.31%3,4 (Cost $187,694,575)		187,694,575			187,694,575
Total Investments, at Value (Cost $7,424,030,130)		100.4%			10,059,494,582
Net Other Assets (Liabilities)		(0.4	)		(36,483,766	)
Net Assets		100.0%		$	10,023,010,816

Footnotes to Statement of Investments

1. Non-income producing security.

2. Security is a Master Limited Partnership.

3. Rate shown is the 7-day yield at period end.

4. Is or was an affiliate, as defined in the Investment Company Act of 1940, as amended, at or during the reporting period, by virtue of the Fund owning at least 5% of the voting securities of the issuer or as a result of the Fund and the issuer having the same investment adviser. Transactions during the reporting period in which the issuer was an affiliate are as follows:

	Shares August 31, 2017		Gross Additions		Gross Reductions		Shares February 28, 2018
Oppenheimer Institutional Government Money Market Fund, Cl. E		34,362,131		1,098,837,088		945,504,644		187,694,575
	Value		Income		Realized Gain (Loss)		Change in Unrealized Gain (Loss)
Oppenheimer Institutional Government Money Market Fund, Cl. E	$	187,694,575	$	1,069,415	$	—	$	—

See accompanying Notes to Financial Statements.

13      OPPENHEIMER MAIN STREET FUND

STATEMENT OF ASSETS AND LIABILITIES February 28, 2018 Unaudited

Assets
Investments, at value—see accompanying statement of investments:
Unaffiliated companies (cost $7,236,335,555)	$	9,871,800,007
Affiliated companies (cost $187,694,575)		187,694,575
		10,059,494,582
Receivables and other assets:
Investments sold		100,840,149
Dividends		8,912,552
Shares of beneficial interest sold		3,226,093
Other		961,299
Total assets		10,173,434,675
Liabilities
Bank overdraft		43,509,369
Payables and other liabilities:
Investments purchased		96,745,084
Shares of beneficial interest redeemed		7,691,609
Distribution and service plan fees		1,641,281
Trustees’ compensation		656,616
Other		179,900
Total liabilities		150,423,859
Net Assets	$	10,023,010,816
Composition of Net Assets
Par value of shares of beneficial interest	$	198,266
Additional paid-in capital		7,047,302,278
Accumulated net investment income		1,464,618
Accumulated net realized gain on investments and foreign currency transactions		338,581,202
Net unrealized appreciation on investments		2,635,464,452
Net Assets	$	10,023,010,816

14      OPPENHEIMER MAIN STREET FUND

Net Asset Value Per Share
Class A Shares:
Net asset value and redemption price per share (based on net assets of $7,435,001,569 and 146,139,597 shares of beneficial interest outstanding)	$	50.88
Maximum offering price per share (net asset value plus sales charge of 5.75% of offering price)	$	53.98
Class B Shares:
Net asset value, redemption price (excludes applicable contingent deferred sales charge) and offering price per share (based on net assets of $13,892,012 and 284,217 shares of beneficial interest outstanding)	$	48.88
Class C Shares:
Net asset value, redemption price (excludes applicable contingent deferred sales charge) and offering price per share (based on net assets of $811,888,099 and 16,843,570 shares of beneficial interest outstanding)	$	48.20
Class I Shares:
Net asset value, redemption price and offering price per share (based on net assets of $727,579,595 and 14,445,073 shares of beneficial interest outstanding)	$	50.37
Class R Shares:
Net asset value, redemption price (excludes applicable contingent deferred sales charge) and offering price per share (based on net assets of $210,695,945 and 4,217,711 shares of beneficial interest outstanding)	$	49.96
Class Y Shares:
Net asset value, redemption price and offering price per share (based on net assets of $823,953,596 and 16,335,758 shares of beneficial interest outstanding)	$	50.44

See accompanying Notes to Financial Statements.

15      OPPENHEIMER MAIN STREET FUND

STATEMENT OF

OPERATIONS For the Six Months Ended February 28, 2018 Unaudited

Investment Income
Dividends:
Unaffiliated companies (net of foreign withholding taxes of $489,583)	$	85,535,728
Affiliated companies		1,069,415
Interest		37,396
Total investment income		86,642,539
Expenses
Management fees		23,125,011
Distribution and service plan fees:
Class A		8,542,361
Class B		118,101
Class C		4,101,652
Class R		502,804
Transfer and shareholder servicing agent fees:
Class A		7,933,959
Class B		25,660
Class C		875,692
Class I		113,672
Class R		216,471
Class Y		855,396
Shareholder communications:
Class A		24,402
Class B		1,334
Class C		3,057
Class I		2,236
Class R		474
Class Y		1,907
Borrowing fees		185,748
Trustees’ compensation		153,674
Custodian fees and expenses		31,931
Other		323,798
Total expenses		47,139,340
Less waivers and reimbursements of expenses		(564,121	)
Net expenses		46,575,219
Net Investment Income		40,067,320
Realized and Unrealized Gain (Loss)
Net realized gain on:
Investment transactions in unaffiliated companies		424,253,712
Foreign currency transactions		27,709
Net realized gain		424,281,421
Net change in unrealized appreciation/depreciation on investment transactions in unaffiliated companies		(67,924,162	)
Net Increase in Net Assets Resulting from Operations	$	396,424,579

See accompanying Notes to Financial Statements.

16      OPPENHEIMER MAIN STREET FUND

STATEMENTS OF CHANGES IN NET ASSETS

	Six Months Ended February 28, 2018 (Unaudited)			Year Ended   August 31, 2017
Operations
Net investment income	$	40,067,320		$	93,318,958
Net realized gain		424,281,421			645,985,492
Net change in unrealized appreciation/depreciation		(67,924,162	)		566,722,334
Net increase in net assets resulting from operations		396,424,579			1,306,026,784
Dividends and/or Distributions to Shareholders
Dividends from net investment income:
Class A		(76,068,319	)		(59,068,015	)
Class B		—			—
Class C		(2,728,065	)		(3,140,270	)
Class I		(10,319,526	)		(10,010,420	)
Class R		(1,776,685	)		(1,236,820	)
Class Y		(10,103,630	)		(8,678,283	)
		(100,996,225	)		(82,133,808	)
Distributions from net realized gain:
Class A		(454,544,150	)		(103,171,052	)
Class B		(1,368,357	)		(1,113,801	)
Class C		(52,975,445	)		(14,060,839	)
Class I		(44,766,718	)		(12,535,678	)
Class R		(12,858,210	)		(2,641,225	)
Class Y		(49,630,719	)		(12,404,503	)
		(616,143,599	)		(145,927,098	)
Beneficial Interest Transactions
Net increase (decrease) in net assets resulting from beneficial interest transactions:
Class A		234,149,226			1,165,143,938
Class B		(22,160,262	)		(42,332,535	)
Class C		11,026,994			28,978,213
Class I		(4,635,408	)		79,024,386
Class R		28,452,359			37,720,326
Class Y		72,365,706			57,472,762
		319,198,615			1,326,007,090
Net Assets
Total increase (decrease)		(1,516,630	)		2,403,972,968
Beginning of period		10,024,527,446			7,620,554,478
End of period (including accumulated net investment income of $1,464,618 and $62,393,523, respectively)		$  10,023,010,816		$	10,024,527,446

See accompanying Notes to Financial Statements.

17      OPPENHEIMER MAIN STREET FUND

FINANCIAL HIGHLIGHTS

Class A	Six Months Ended February 28, 2018 (Unaudited)		Year Ended August 31, 2017		Year Ended August 31, 2016		Year Ended August 31, 2015		Year Ended August 29, 20141		Year Ended August 30, 20131
Per Share Operating Data
Net asset value, beginning of period		$52.61		$46.57		$47.64		$52.73		$42.39		$36.69
Income (loss) from investment operations:
Net investment income2		0.21		0.53		0.50		0.35		0.29		0.37
Net realized and unrealized gain		1.89		6.90		4.41		0.26		10.36		5.73
Total from investment operations		2.10		7.43		4.91		0.61		10.65		6.10
Dividends and/or distributions to shareholders:
Dividends from net investment income		(0.55)		(0.51)		(0.43)		(0.35)		(0.31)		(0.40)
Distributions from net realized gain		(3.28)		(0.88)		(5.55)		(5.35)		0.00		0.00
Total dividends and/or distributions to shareholders		(3.83)		(1.39)		(5.98)		(5.70)		(0.31)		(0.40)
Net asset value, end of period		$50.88		$52.61		$46.57		$47.64		$52.73		$42.39
Total Return, at Net Asset Value3		3.98%		16.27%		11.22%		0.99%		25.20%		16.78%
Ratios/Supplemental Data
Net assets, end of period (in thousands)		$7,435,001		$7,436,792		$5,488,385		$5,163,000		$5,429,874		$4,588,619
Average net assets (in thousands)		$7,555,230		$6,450,132		$5,225,636		$5,404,461		$5,096,996		$4,494,340
Ratios to average net assets:4
Net investment income		0.81%		1.08%		1.12%		0.70%		0.60%		0.95%
Expenses excluding specific expenses listed below		0.91%		0.93%		0.93%		0.93%		0.92%		0.93%
Interest and fees from borrowings		0.00%5		0.00%5		0.00%5		0.00%5		0.00%		0.00%
Total expenses6		0.91%		0.93%		0.93%		0.93%		0.92%		0.93%
Expenses after payments, waivers and/or reimbursements and reduction to custodian expenses		0.90%		0.91%		0.93%7		0.93%7		0.92%7		0.93%7
Portfolio turnover rate		22%		40%		39%		43%		52%		46%

18      OPPENHEIMER MAIN STREET FUND

1. Represents the last business day of the Fund’s reporting period.

2. Per share amounts calculated based on the average shares outstanding during the period.

3. Assumes an initial investment on the business day before the first day of the fiscal period, with all dividends and distributions reinvested in additional shares on the reinvestment date, and redemption at the net asset value calcu-lated on the last business day of the fiscal period. Sales charges are not reflected in the total returns. Total returns are not annualized for periods less than one full year. Returns do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

4. Annualized for periods less than one full year.

5. Less than 0.005%.

6. Total expenses including indirect expenses from affiliated fund fees and expenses were as follows:

Six Months Ended February 28, 2018	0.91	%
Year Ended August 31, 2017	0.93	%
Year Ended August 31, 2016	0.93	%
Year Ended August 31, 2015	0.93	%
Year Ended August 29, 2014	0.92	%
Year Ended August 30, 2013	0.93	%

7. Waiver was less than 0.005%.

See accompanying Notes to Financial Statements.

19      OPPENHEIMER MAIN STREET FUND

FINANCIAL HIGHLIGHTS Continued

Class B	Six Months Ended February 28, 2018 (Unaudited)		Year Ended August 31, 2017		Year Ended August 31, 2016		Year Ended August 31, 2015		Year Ended August 29, 20141		Year Ended August 30, 20131
Per Share Operating Data
Net asset value, beginning of period		$50.35		$44.48		$45.65		$50.78		$40.88		$35.33
Income (loss) from investment operations:
Net investment income (loss)2		0.01		0.16		0.16		(0.02)		(0.10)		0.01
Net realized and unrealized gain		1.80		6.59		4.22		0.24		10.00		5.54
Total from investment operations		1.81		6.75		4.38		0.22		9.90		5.55
Dividends and/or distributions to shareholders:
Dividends from net investment income		0.00		0.00		0.00		0.00		0.00		0.00
Distributions from net realized gain		(3.28)		(0.88)		(5.55)		(5.35)		0.00		0.00
Total dividends and/or distributions to shareholders		(3.28)		(0.88)		(5.55)		(5.35)		0.00		0.00
Net asset value, end of period		$48.88		$50.35		$44.48		$45.65		$50.78		$40.88
Total Return, at Net Asset Value3		3.58%		15.40%		10.38%		0.21%		24.22%		15.71%
Ratios/Supplemental Data
Net assets, end of period (in thousands)		$13,892		$36,182		$72,373		$113,578		$185,705		$205,386
Average net assets (in thousands)		$23,972		$52,268		$90,264		$148,294		$199,044		$224,582
Ratios to average net assets:4
Net investment income (loss)		0.04%		0.35%		0.38%		(0.05)%		(0.22)%		0.02%
Expenses excluding specific expenses listed below		1.69%		1.69%		1.69%		1.68%		1.74%		1.92%
Interest and fees from borrowings		0.00%5		0.00%5		0.00%5		0.00%5		0.00%		0.00%
Total expenses6		1.69%		1.69%		1.69%		1.68%		1.74%		1.92%
Expenses after payments, waivers and/or reimbursements and reduction to custodian expenses		1.68%		1.68%		1.69%7		1.68%7		1.73%		1.86%
Portfolio turnover rate		22%		40%		39%		43%		52%		46%

20      OPPENHEIMER MAIN STREET FUND

1. Represents the last business day of the Fund’s reporting period.

2. Per share amounts calculated based on the average shares outstanding during the period.

3. Assumes an initial investment on the business day before the first day of the fiscal period, with all dividends and distributions reinvested in additional shares on the reinvestment date, and redemption at the net asset value calcu-lated on the last business day of the fiscal period. Sales charges are not reflected in the total returns. Total returns are not annualized for periods less than one full year. Returns do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

4. Annualized for periods less than one full year.

5. Less than 0.005%.

6. Total expenses including indirect expenses from affiliated fund fees and expenses were as follows:

Six Months Ended February 28, 2018	1.69	%
Year Ended August 31, 2017	1.69	%
Year Ended August 31, 2016	1.69	%
Year Ended August 31, 2015	1.68	%
Year Ended August 29, 2014	1.74	%
Year Ended August 30, 2013	1.92	%

7. Waiver was less than 0.005%.

See accompanying Notes to Financial Statements.

21      OPPENHEIMER MAIN STREET FUND

FINANCIAL HIGHLIGHTS Continued

Class C	Six Months Ended February 28, 2018 (Unaudited)		Year Ended August 31, 2017		Year Ended August 31, 2016		Year Ended August 31, 2015		Year Ended August 29, 20141		Year Ended August 30, 20131
Per Share Operating Data
Net asset value, beginning of period		$49.85		$44.24		$45.51		$50.63		$40.74		$35.22
Income (loss) from investment operations:
Net investment income (loss)2		0.01		0.15		0.16		(0.02)		(0.07)		0.07
Net realized and unrealized gain		1.79		6.54		4.21		0.25		9.96		5.53
Total from investment operations		1.80		6.69		4.37		0.23		9.89		5.60
Dividends and/or distributions to shareholders:
Dividends from net investment income		(0.17)		(0.20)		(0.09)		0.00		0.00		(0.08)
Distributions from net realized gain		(3.28)		(0.88)		(5.55)		(5.35)		0.00		0.00
Total dividends and/or distributions to shareholders		(3.45)		(1.08)		(5.64)		(5.35)		0.00		(0.08)
Net asset value, end of period		$48.20		$49.85		$44.24		$45.51		$50.63		$40.74
Total Return, at Net Asset Value3		3.59%		15.39%		10.39%		0.23%		24.28%		15.92%
Ratios/Supplemental Data
Net assets, end of period (in thousands)		$811,888		$826,928		$705,167		$641,863		$677,274		$582,360
Average net assets (in thousands)		$833,583		$773,972		$660,113		$670,954		$641,903		$568,419
Ratios to average net assets:4
Net investment income (loss)		0.05%		0.32%		0.36%		(0.05)%		(0.15)%		0.20%
Expenses excluding specific expenses listed below		1.67%		1.68%		1.69%		1.68%		1.67%		1.68%
Interest and fees from borrowings		0.00%5		0.00%5		0.00%5		0.00%5		0.00%		0.00%
Total expenses6		1.67%		1.68%		1.69%		1.68%		1.67%		1.68%
Expenses after payments, waivers and/or reimbursements and reduction to custodian expenses		1.66%		1.67%		1.69%7		1.68%7		1.67%7		1.68%7
Portfolio turnover rate		22%		40%		39%		43%		52%		46%

22      OPPENHEIMER MAIN STREET FUND

1. Represents the last business day of the Fund’s reporting period.

2. Per share amounts calculated based on the average shares outstanding during the period.

3. Assumes an initial investment on the business day before the first day of the fiscal period, with all dividends and distributions reinvested in additional shares on the reinvestment date, and redemption at the net asset value calcu-lated on the last business day of the fiscal period. Sales charges are not reflected in the total returns. Total returns are not annualized for periods less than one full year. Returns do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

4. Annualized for periods less than one full year.

5. Less than 0.005%.

6. Total expenses including indirect expenses from affiliated fund fees and expenses were as follows:

Six Months Ended February 28, 2018	1.67	%
Year Ended August 31, 2017	1.68	%
Year Ended August 31, 2016	1.69	%
Year Ended August 31, 2015	1.68	%
Year Ended August 29, 2014	1.67	%
Year Ended August 30, 2013	1.68	%

7. Waiver was less than 0.005%.

See accompanying Notes to Financial Statements.

23      OPPENHEIMER MAIN STREET FUND

FINANCIAL HIGHLIGHTS Continued

Class I	Six Months Ended February 28, 2018 (Unaudited)		Year Ended August 31, 2017		Year Ended August 31, 2016		Year Ended August 31, 2015		Year Ended August 29, 20141		Year Ended August 30, 20131
Per Share Operating Data
Net asset value, beginning of period		$52.22		$46.25		$47.36		$52.47		$42.33		$36.82
Income (loss) from investment operations:
Net investment income2		0.31		0.73		0.67		0.56		0.51		0.50
Net realized and unrealized gain		1.88		6.83		4.42		0.25		10.30		5.75
Total from investment operations		2.19		7.56		5.09		0.81		10.81		6.25
Dividends and/or distributions to shareholders:
Dividends from net investment income		(0.76)		(0.71)		(0.65)		(0.57)		(0.67)		(0.74)
Distributions from net realized gain		(3.28)		(0.88)		(5.55)		(5.35)		0.00		0.00
Total dividends and/or distributions to shareholders		(4.04)		(1.59)		(6.20)		(5.92)		(0.67)		(0.74)
Net asset value, end of period		$50.37		$52.22		$46.25		$47.36		$52.47		$42.33
Total Return, at Net Asset Value3		4.19%		16.76%		11.72%		1.41%		25.73%		17.28%
Ratios/Supplemental Data
Net assets, end of period (in thousands)		$727,580		$756,378		$589,459		$277,749		$295,519		$25,203
Average net assets (in thousands)		$763,813		$698,501		$335,376		$288,411		$203,534		$15,305
Ratios to average net assets:4
Net investment income		1.21%		1.49%		1.50%		1.13%		1.05%		1.26%
Expenses excluding specific expenses listed below		0.50%		0.50%		0.50%		0.50%		0.50%		0.51%
Interest and fees from borrowings		0.00%5		0.00%5		0.00%5		0.00%5		0.00%		0.00%
Total expenses6		0.50%		0.50%		0.50%		0.50%		0.50%		0.51%
Expenses after payments, waivers and/or reimbursements and reduction to custodian expenses		0.50%7		0.50%7		0.50%7		0.50%7		0.50%7		0.51%7
Portfolio turnover rate		22%		40%		39%		43%		52%		46%

24      OPPENHEIMER MAIN STREET FUND

1. Represents the last business day of the Fund’s reporting period.

2. Per share amounts calculated based on the average shares outstanding during the period.

3. Assumes an initial investment on the business day before the first day of the fiscal period, with all dividends and distributions reinvested in additional shares on the reinvestment date, and redemption at the net asset value calcu-lated on the last business day of the fiscal period. Sales charges are not reflected in the total returns. Total returns are not annualized for periods less than one full year. Returns do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

4. Annualized for periods less than one full year.

5. Less than 0.005%.

6. Total expenses including indirect expenses from affiliated fund fees and expenses were as follows:

Six Months Ended February 28, 2018	0.50%
Year Ended August 31, 2017	0.50%
Year Ended August 31, 2016	0.50%
Year Ended August 31, 2015	0.50%
Year Ended August 29, 2014	0.50%
Year Ended August 30, 2013	0.51%

7. Waiver was less than 0.005%.

See accompanying Notes to Financial Statements.

25      OPPENHEIMER MAIN STREET FUND

FINANCIAL HIGHLIGHTS Continued

Class R	Six Months Ended February 28, 2018 (Unaudited)		Year Ended August 31, 2017		Year Ended August 31, 2016		Year Ended August 31, 2015		Year Ended August 29, 20141		Year Ended August 30, 20131
Per Share Operating Data
Net asset value, beginning of period		$51.70		$45.82		$46.95		$52.05		$41.85		$36.17
Income (loss) from investment operations:
Net investment income2		0.14		0.40		0.38		0.22		0.16		0.26
Net realized and unrealized gain		1.85		6.77		4.36		0.26		10.23		5.66
Total from investment operations		1.99		7.17		4.74		0.48		10.39		5.92
Dividends and/or distributions to shareholders:
Dividends from net investment income		(0.45)		(0.41)		(0.32)		(0.23)		(0.19)		(0.24)
Distributions from net realized gain		(3.28)		(0.88)		(5.55)		(5.35)		0.00		0.00
Total dividends and/or distributions to shareholders		(3.73)		(1.29)		(5.87)		(5.58)		(0.19)		(0.24)
Net asset value, end of period		$49.96		$51.70		$45.82		$46.95		$52.05		$41.85
Total Return, at Net Asset Value3		3.82%		15.99%		10.94%		0.73%		24.88%		16.47%
Ratios/Supplemental Data
Net assets, end of period (in thousands)		$210,696		$189,337		$132,365		$115,038		$118,479		$105,630
Average net assets (in thousands)		$206,640		$158,013		$119,719		$118,942		$114,029		$104,731
Ratios to average net assets:4
Net investment income		0.56%		0.82%		0.86%		0.45%		0.34%		0.68%
Expenses excluding specific expenses listed below		1.17%		1.18%		1.19%		1.18%		1.17%		1.20%
Interest and fees from borrowings		0.00%5		0.00%5		0.00%5		0.00%5		0.00%		0.00%
Total expenses6		1.17%		1.18%		1.19%		1.18%		1.17%		1.20%
Expenses after payments, waivers and/or reimbursements and reduction to custodian expenses		1.16%		1.17%		1.19%7		1.18%7		1.17%7		1.20%7
Portfolio turnover rate		22%		40%		39%		43%		52%		46%

26      OPPENHEIMER MAIN STREET FUND

1. Represents the last business day of the Fund’s reporting period.

2. Per share amounts calculated based on the average shares outstanding during the period.

3. Assumes an initial investment on the business day before the first day of the fiscal period, with all dividends and distributions reinvested in additional shares on the reinvestment date, and redemption at the net asset value calcu-lated on the last business day of the fiscal period. Sales charges are not reflected in the total returns. Total returns are not annualized for periods less than one full year. Returns do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

4. Annualized for periods less than one full year.

5. Less than 0.005%.

6. Total expenses including indirect expenses from affiliated fund fees and expenses were as follows:

Six Months Ended February 28, 2018	1.17	%
Year Ended August 31, 2017	1.18	%
Year Ended August 31, 2016	1.19	%
Year Ended August 31, 2015	1.18	%
Year Ended August 29, 2014	1.17	%
Year Ended August 30, 2013	1.20	%

7. Waiver was less than 0.005%.

See accompanying Notes to Financial Statements.

27      OPPENHEIMER MAIN STREET FUND

FINANCIAL HIGHLIGHTS Continued

Class Y	Six Months Ended February 28, 2018 (Unaudited)		Year Ended August 31, 2017		Year Ended August 31, 2016		Year Ended August 31, 2015		Year Ended August 29, 20141		Year Ended August 30, 20131
Per Share Operating Data
Net asset value, beginning of period		$52.25		$46.26		$47.37		$52.48		$42.30		$36.81
Income (loss) from investment operations:
Net investment income2		0.27		0.64		0.62		0.46		0.40		0.49
Net realized and unrealized gain		1.87		6.85		4.37		0.26		10.32		5.72
Total from investment operations		2.14		7.49		4.99		0.72		10.72		6.21
Dividends and/or distributions to shareholders:
Dividends from net investment income		(0.67)		(0.62)		(0.55)		(0.48)		(0.54)		(0.72)
Distributions from net realized gain		(3.28)		(0.88)		(5.55)		(5.35)		0.00		0.00
Total dividends and/or distributions to shareholders		(3.95)		(1.50)		(6.10)		(5.83)		(0.54)		(0.72)
Net asset value, end of period		$50.44		$52.25		$46.26		$47.37		$52.48		$42.30
Total Return, at Net Asset Value3		4.09%		16.55%		11.49%		1.23%		25.52%		17.18%
Ratios/Supplemental Data
Net assets, end of period (in thousands)		$823,954		$778,910		$632,805		$664,474		$664,996		$723,798
Average net assets (in thousands)		$815,489		$725,736		$618,333		$693,669		$655,922		$469,824
Ratios to average net assets:4
Net investment income		1.04%		1.32%		1.39%		0.94%		0.84%		1.21%
Expenses excluding specific expenses listed below		0.68%		0.69%		0.69%		0.69%		0.67%		0.61%
Interest and fees from borrowings		0.00%5		0.00%5		0.00%5		0.00%5		0.00%		0.00%
Total expenses6		0.68%		0.69%		0.69%		0.69%		0.67%		0.61%
Expenses after payments, waivers and/or reimbursements and reduction to custodian expenses		0.67%		0.68%		0.69%7		0.69%7		0.67%7		0.61%7
Portfolio turnover rate		22%		40%		39%		43%		52%		46%

28      OPPENHEIMER MAIN STREET FUND

1. Represents the last business day of the Fund’s reporting period.

2. Per share amounts calculated based on the average shares outstanding during the period.

3. Assumes an initial investment on the business day before the first day of the fiscal period, with all dividends and distributions reinvested in additional shares on the reinvestment date, and redemption at the net asset value calcu-lated on the last business day of the fiscal period. Sales charges are not reflected in the total returns. Total returns are not annualized for periods less than one full year. Returns do not reflect the deduction of taxes that a shareholder would pay on fund distributions or the redemption of fund shares.

4. Annualized for periods less than one full year.

5. Less than 0.005%.

6. Total expenses including indirect expenses from affiliated fund fees and expenses were as follows:

Six Months Ended February 28, 2018	0.68	%
Year Ended August 31, 2017	0.69	%
Year Ended August 31, 2016	0.69	%
Year Ended August 31, 2015	0.69	%
Year Ended August 29, 2014	0.67	%
Year Ended August 30, 2013	0.61	%

7. Waiver was less than 0.005%.

See accompanying Notes to Financial Statements.

29      OPPENHEIMER MAIN STREET FUND

NOTES TO FINANCIAL STATEMENTS February 28, 2018 Unaudited

1. Organization

Oppenheimer Main Street Fund (the “Fund”) is a separate series of Oppenheimer Main

Street Funds, a diversified open-end management investment company registered under the Investment Company Act of 1940 (“1940 Act”), as amended. The Fund’s investment objective is to seek capital appreciation. The Fund’s investment adviser is OFI Global Asset Management, Inc. (“OFI Global” or the “Manager”), a wholly-owned subsidiary of OppenheimerFunds, Inc. (“OFI” or the “Sub-Adviser”). The Manager has entered into a sub-advisory agreement with OFI.

The Fund offers Class A, Class C, Class I, Class R and Class Y shares, and previously offered Class B shares for new purchase through June 29, 2012. Subsequent to that date, no new purchases of Class B shares are permitted, however reinvestment of dividend and/or capital gain distributions and exchanges of Class B shares into and from other Oppenheimer funds are allowed. Class A shares are sold at their offering price, which is normally net asset value plus a front-end sales charge. Class C and Class R shares are sold, and Class B shares were sold, without a front-end sales charge but may be subject to a contingent deferred sales charge (“CDSC”). Class R shares are sold only through retirement plans. Retirement plans that offer Class R shares may impose charges on those accounts. Class I and Class Y shares are sold to certain institutional investors or intermediaries without either a front-end sales charge or a CDSC, however, the intermediaries may impose charges on their accountholders who beneficially own Class I and Class Y shares. All classes of shares have identical rights and voting privileges with respect to the Fund in general and exclusive voting rights on matters that affect that class alone. Earnings, net assets and net asset value per share may differ due to each class having its own expenses, such as transfer and shareholder servicing agent fees and shareholder communications, directly attributable to that class. Class A, B, C and R shares have separate distribution and/or service plans under which they pay fees. Class I and Class Y shares do not pay such fees. Class B shares will automatically convert to Class A shares 72 months after the date of purchase.

The following is a summary of significant accounting policies followed in the Fund’s preparation of financial statements in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”).

2. Significant Accounting Policies

Security Valuation. All investments in securities are recorded at their estimated fair value, as described in Note 3.

Foreign Currency Translation. The books and records of the Fund are maintained in U.S. dollars. Any foreign currency amounts are translated into U.S. dollars on the following basis:

(1) Value of investment securities, other assets and liabilities — at the exchange rates prevailing at Market Close as described in Note 3.

(2) Purchases and sales of investment securities, income and expenses — at the rates of exchange prevailing on the respective dates of such transactions.

Although the net assets and the values are presented at the foreign exchange rates at

30      OPPENHEIMER MAIN STREET FUND

2. Significant Accounting Policies (Continued)

Market Close, the Fund does not isolate the portion of the results of operations resulting from changes in foreign exchange rates on investments from the fluctuations arising from changes in prices of securities held. Such fluctuations are included with the net realized and unrealized gains or losses from investments shown in the Statement of Operations.

For securities, which are subject to foreign withholding tax upon disposition, realized gains or losses on such securities are recorded net of foreign withholding tax.

Reported net realized foreign exchange gains or losses arise from sales of foreign currencies, currency gains or losses realized between the trade and settlement dates on securities transactions, the difference between the amounts of dividends, interest, and foreign withholding tax reclaims recorded on the Fund’s books, and the U.S. dollar equivalent of

the amounts actually received or paid. Net unrealized foreign exchange gains and losses arise from changes in the value of assets and liabilities other than investments in securities, resulting from changes in the exchange rate.

Allocation of Income, Expenses, Gains and Losses. Income, expenses (other than those attributable to a specific class), gains and losses are allocated on a daily basis to each class of shares based upon the relative proportion of net assets represented by such class. Operating expenses directly attributable to a specific class are charged against the operations of that class.

Dividends and Distributions to Shareholders. Dividends and distributions to shareholders, which are determined in accordance with income tax regulations and may differ from U.S. GAAP, are recorded on the ex-dividend date. Income and capital gain distributions, if any, are declared and paid annually or at other times as determined necessary by the Manager.

The tax character of distributions is determined as of the Fund’s fiscal year end. Therefore, a portion of the Fund’s distributions made to shareholders prior to the Fund’s fiscal year end may ultimately be categorized as a tax return of capital.

Investment Income. Dividend income is recorded on the ex-dividend date or upon ex-dividend notification in the case of certain foreign dividends where the ex-dividend date may have passed. Non-cash dividends included in dividend income, if any, are recorded at the fair value of the securities received. Withholding taxes on foreign dividends, if any, and capital gains taxes on foreign investments, if any, have been provided for in accordance with the Fund’s understanding of the applicable tax rules and regulations. Interest income, if any, is recognized on an accrual basis. Discount and premium, which are included in interest income on the Statement of Operations, are amortized or accreted daily.

Return of Capital Estimates. Distributions received from the Fund’s investments in Master Limited Partnerships (MLPs) and Real Estate Investments Trusts (REITs), generally are comprised of income and return of capital. The Fund records investment income and return of capital based on estimates. Such estimates are based on historical information available

31      OPPENHEIMER MAIN STREET FUND

NOTES TO FINANCIAL STATEMENTS Unaudited / Continued

2. Significant Accounting Policies (Continued)

from each MLP, REIT and other industry sources. These estimates may subsequently be revised based on information received from MLPs and REITs after their tax reporting periods are concluded.

Custodian Fees. “Custodian fees and expenses” in the Statement of Operations may include interest expense incurred by the Fund on any cash overdrafts of its custodian account during the period. Such cash overdrafts may result from the effects of failed trades in portfolio securities and from cash outflows resulting from unanticipated shareholder redemption activity. The Fund pays interest to its custodian on such cash overdrafts, to the extent they are not offset by positive cash balances maintained by the Fund, based on the negative rolling average balance at an average Federal Funds Rate plus 0.50%. The “Reduction to custodian expenses” line item, if applicable, represents earnings on cash balances maintained by the Fund during the period. Such interest expense and other custodian fees may be paid with these earnings.

Security Transactions. Security transactions are recorded on the trade date. Realized gains and losses on securities sold are determined on the basis of identified cost.

Indemnifications. The Fund’s organizational documents provide current and former Trustees and officers with a limited indemnification against liabilities arising in connection with the performance of their duties to the Fund. In the normal course of business, the Fund may also enter into contracts that provide general indemnifications. The Fund’s maximum exposure under these arrangements is unknown as this would be dependent on future claims that may be made against the Fund. The risk of material loss from such claims is considered remote.

Federal Taxes. The Fund intends to comply with provisions of the Internal Revenue Code applicable to regulated investment companies and to distribute substantially all of its investment company taxable income to shareholders. Therefore, no federal income or excise tax provision is required. The Fund files income tax returns in U.S. federal and applicable state jurisdictions. The statute of limitations on the Fund’s tax return filings generally remains open for the three preceding fiscal reporting period ends. The Fund has analyzed its tax positions for the fiscal year ended August 31, 2017, including open tax years, and does not believe there are any uncertain tax positions requiring recognition in the Fund’s financial statements.

During the fiscal year ended August 31, 2017, the Fund utilized $157,584 of capital loss carryforwards to offset capital gains realized in that fiscal year. The Fund had $3,256,724 of straddle losses which were deferred. Capital loss carryforwards with no expiration, if any, must be utilized prior to those with expiration dates. Capital losses with no expiration will be carried forward to future years if not offset by gains.

At period end, it is estimated that the capital loss carryforwards would be zero. The estimated capital loss carryforward represents the carryforward as of the end of the last fiscal year, increased or decreased by capital losses or gains realized in the first six months of the current fiscal year. During the reporting period, it is estimated that the Fund will utilize

32      OPPENHEIMER MAIN STREET FUND

2. Significant Accounting Policies (Continued)

$3,256,724 of capital loss carryforward to offset realized capital gains.

Net investment income (loss) and net realized gain (loss) may differ for financial statement and tax purposes. The character of dividends and distributions made during the fiscal year from net investment income or net realized gains are determined in accordance with federal income tax requirements, which may differ from the character of net investment income or net realized gains presented in those financial statements in accordance with U.S. GAAP. Also, due to timing of dividends and distributions, the fiscal year in which amounts are distributed may differ from the fiscal year in which the income or net realized gain was recorded by the Fund.

The aggregate cost of securities and other investments and the composition of unrealized appreciation and depreciation of securities and other investments for federal income tax purposes at period end are noted in the following table. The primary difference between book and tax appreciation or depreciation of securities and other investments, if applicable, is attributable to the tax deferral of losses or tax realization of financial statement unrealized gain or loss.

Federal tax cost of securities	$	7,429,845,356
Gross unrealized appreciation	$	2,986,803,848
Gross unrealized depreciation		(357,154,622)
Net unrealized appreciation	$	2,629,649,226

Use of Estimates. The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of increases and decreases in net assets from operations during the reporting period. Actual results could differ from those estimates.

3. Securities Valuation

The Fund calculates the net asset value of its shares as of 4:00 P.M. Eastern time, on each day the New York Stock Exchange (the “Exchange”) is open for trading, except in the case of a scheduled early closing of the Exchange, in which case the Fund will calculate net asset value of the shares as of the scheduled early closing time of the Exchange.

The Fund’s Board has adopted procedures for the valuation of the Fund’s securities and has delegated the day-to-day responsibility for valuation determinations under those procedures to the Manager. The Manager has established a Valuation Committee which is responsible for determining a fair valuation for any security for which market quotations are not readily available. The Valuation Committee’s fair valuation determinations are subject to review, approval and ratification by the Fund’s Board at least quarterly or more frequently, if necessary.

Valuation Methods and Inputs

Securities are valued primarily using unadjusted quoted market prices, when available, as supplied by third party pricing services or broker-dealers.

33      OPPENHEIMER MAIN STREET FUND

NOTES TO FINANCIAL STATEMENTS Unaudited / Continued

3. Securities Valuation (Continued)

The following methodologies are used to determine the market value or the fair value of the types of securities described below:

Equity securities traded on a securities exchange (including exchange-traded derivatives other than futures and futures options) are valued based on the official closing price on the principal exchange on which the security is traded, as identified by the Manager, prior to the time when the Fund’s assets are valued. If the official closing price is unavailable, the security is valued at the last sale price on the principal exchange on which it is traded, or if no sales occurred, the security is valued at the mean between the quoted bid and asked prices. Over-the-counter equity securities are valued at the last published sale price, or if no sales occurred, at the mean between the quoted bid and asked prices. Events occurring after the close of trading on foreign exchanges may result in adjustments to the valuation of foreign securities to more accurately reflect their fair value as of the time when the Fund’s assets are valued.

Shares of a registered investment company that are not traded on an exchange are valued at that investment company’s net asset value per share.

Securities for which market quotations are not readily available, or when a significant event has occurred that would materially affect the value of the security, are fair valued either (i) by a standardized fair valuation methodology applicable to the security type or the significant event as previously approved by the Valuation Committee and the Fund’s Board or (ii) as determined in good faith by the Manager’s Valuation Committee. The Valuation Committee considers all relevant facts that are reasonably available, through either public information or information available to the Manager, when determining the fair value of a security. Those standardized fair valuation methodologies include, but are not limited to, valuing securities at the last sale price or initially at cost and subsequently adjusting the value based on: changes in company specific fundamentals, changes in an appropriate securities index, or changes in the value of similar securities which may be further adjusted for any discounts related to security-specific resale restrictions. When possible, such methodologies use observable market inputs such as unadjusted quoted prices of similar securities, observable interest rates, currency rates and yield curves. The methodologies used for valuing securities are not necessarily an indication of the risks associated with investing in those securities nor can it be assured that the Fund can obtain the fair value assigned to a security if it were to sell the security.

Classifications

Each investment asset or liability of the Fund is assigned a level at measurement date based on the significance and source of the inputs to its valuation. Various data inputs may be used in determining the value of each of the Fund’s investments as of the reporting period end.

These data inputs are categorized in the following hierarchy under applicable financial accounting standards:

1) Level 1-unadjusted quoted prices in active markets for identical assets or liabilities (including securities actively traded on a securities exchange)

2) Level 2-inputs other than unadjusted quoted prices that are observable for the asset or liability (such as unadjusted quoted prices for similar assets and market corroborated inputs

34      OPPENHEIMER MAIN STREET FUND

3. Securities Valuation (Continued)

such as interest rates, prepayment speeds, credit risks, etc.)

3) Level 3-significant unobservable inputs (including the Manager’s own judgments about assumptions that market participants would use in pricing the asset or liability).

The inputs used for valuing securities are not necessarily an indication of the risks associated with investing in those securities.

The Fund classifies each of its investments in investment companies which are publicly offered as Level 1. Investment companies that are not publicly offered, if any, are classified as Level 2 in the fair value hierarchy.

The table below categorizes amounts that are included in the Fund’s Statement of Assets and Liabilities at period end based on valuation input level:

	Level 1— Unadjusted Quoted Prices		Level 2— Other Significant Observable Inputs		Level 3— Significant Unobservable Inputs		Value
Assets Table
Investments, at Value:
Common Stocks
Consumer Discretionary	$	1,084,480,763	$	—		$                —	$	1,084,480,763
Consumer Staples		745,958,909		—		—		745,958,909
Energy		525,951,570		—		—		525,951,570
Financials		1,986,881,110		—		—		1,986,881,110
Health Care		1,406,421,678		—		—		1,406,421,678
Industrials		935,572,807		—		—		935,572,807
Information Technology		2,523,774,616		—		—		2,523,774,616
Materials		293,442,609		—		—		293,442,609
Telecommunication Services		130,397,991		—		—		130,397,991
Utilities		94,521,792		144,396,162		—		238,917,954
Investment Company		187,694,575		—		—		187,694,575
Total Assets	$	9,915,098,420	$	144,396,162		$                —	$	10,059,494,582

Forward currency exchange contracts and futures contracts, if any, are reported at their unrealized appreciation/depreciation at measurement date, which represents the change in the contract’s value from trade date. All additional assets and liabilities included in the above table are reported at their market value at measurement date.

4. Investments and Risks

Investments in Affiliated Funds. The Fund is permitted to invest in other mutual funds advised by the Manager (“Affiliated Funds”). Affiliated Funds are open-end management investment companies registered under the 1940 Act, as amended. The Manager is the investment adviser of, and the Sub-Adviser provides investment and related advisory services to, the Affiliated Funds. When applicable, the Fund’s investments in Affiliated Funds are included in the Statement of Investments. Shares of Affiliated Funds are valued at their net asset value per share. As a shareholder, the Fund is subject to its proportional share of the

35      OPPENHEIMER MAIN STREET FUND

NOTES TO FINANCIAL STATEMENTS Unaudited / Continued

4. Investments and Risks (Continued)

Affiliated Funds’ expenses, including their management fee. The Manager will waive fees and/ or reimburse Fund expenses in an amount equal to the indirect management fees incurred through the Fund’s investment in the Affiliated Funds.

Each of the Affiliated Funds in which the Fund invests has its own investment risks, and those risks can affect the value of the Fund’s investments and therefore the value of the Fund’s shares. To the extent that the Fund invests more of its assets in one Affiliated Fund than in another, the Fund will have greater exposure to the risks of that Affiliated Fund.

Investments in Money Market Instruments. The Fund is permitted to invest its free cash balances in money market instruments to provide liquidity or for defensive purposes. The Fund may invest in money market instruments by investing in Class E shares of Oppenheimer Institutional Government Money Market Fund (“IGMMF”), which is an Affiliated Fund. IGMMF is regulated as a money market fund under the 1940 Act, as amended. The Fund may also invest in money market instruments directly or in other affiliated or unaffiliated money market funds.

Master Limited Partnerships (“MLPs”). MLPs issue common units that represent an equity ownership interest in a partnership and provide limited voting rights. MLP common units are registered with the Securities and Exchange Commission (“SEC”), and are freely tradable on securities exchanges such as the NYSE and the NASDAQ Stock Market (“NASDAQ”), or in the over-the-counter (“OTC”) market. An MLP consists of one or more general partners, who conduct the business, and one or more limited partners, who contribute capital. MLP common unit holders have a limited role in the partnership’s operations and management. The Fund, as a limited partner, normally would not be liable for the debts of the MLP beyond the amounts the Fund has contributed, but would not be shielded to the same extent that a shareholder of a corporation would be. In certain circumstances creditors of an MLP would have the right to seek return of capital distributed to a limited partner. This right of an MLP’s creditors would continue after the Fund sold its investment in the MLP.

Equity Security Risk. Stocks and other equity securities fluctuate in price. The value of the Fund’s portfolio may be affected by changes in the equity markets generally. Equity markets may experience significant short-term volatility and may fall sharply at times. Different markets may behave differently from each other and U.S. equity markets may move in the opposite direction from one or more foreign stock markets. Adverse events in any part of the equity or fixed-income markets may have unexpected negative effects on other market segments.

The prices of individual equity securities generally do not all move in the same direction at the same time and a variety of factors can affect the price of a particular company’s securities. These factors may include, but are not limited to, poor earnings reports, a loss of customers, litigation against the company, general unfavorable performance of the company’s sector or industry, or changes in government regulations affecting the company or its industry.

36      OPPENHEIMER MAIN STREET FUND

5. Market Risk Factors

The Fund’s investments in securities and/or financial derivatives may expose the Fund to various market risk factors:

Commodity Risk. Commodity risk relates to the change in value of commodities or commodity indexes as they relate to increases or decreases in the commodities market. Commodities are physical assets that have tangible properties. Examples of these types of assets are crude oil, heating oil, metals, livestock, and agricultural products.

Credit Risk. Credit risk relates to the ability of the issuer of debt to meet interest and principal payments, or both, as they come due. In general, lower-grade, higher-yield debt securities are subject to credit risk to a greater extent than lower-yield, higher-quality securities.

Equity Risk. Equity risk relates to the change in value of equity securities as they relate to increases or decreases in the general market.

Foreign Exchange Rate Risk. Foreign exchange rate risk relates to the change in the U.S. dollar value of a security held that is denominated in a foreign currency. The U.S. dollar value of a foreign currency denominated security will decrease as the dollar appreciates against the currency, while the U.S. dollar value will increase as the dollar depreciates against the currency.

Interest Rate Risk. Interest rate risk refers to the fluctuations in value of fixed-income securities resulting from the inverse relationship between price and yield. For example, an increase in general interest rates will tend to reduce the market value of already issued fixed-income investments, and a decline in general interest rates will tend to increase their value. In addition, debt securities with longer maturities, which tend to have higher yields, are subject to potentially greater fluctuations in value from changes in interest rates than obligations with shorter maturities.

Volatility Risk. Volatility risk refers to the magnitude of the movement, but not the direction of the movement, in a financial instrument’s price over a defined time period. Large increases or decreases in a financial instrument’s price over a relative time period typically indicate greater volatility risk, while small increases or decreases in its price typically indicate lower volatility risk.

6. Shares of Beneficial Interest

The Fund has authorized an unlimited number of $0.001 par value shares of beneficial interest of each class. Transactions in shares of beneficial interest were as follows:

	Six Months Ended February 28, 2018						Year Ended August 31, 2017
	Shares			Amount			Shares			Amount
Class A
Sold		4,005,258		$	210,727,082			11,716,093		$	569,095,534
Dividends and/or distributions reinvested		10,080,262			512,984,520			3,329,489			156,952,147
Acquisition—Note 10		—			—			28,125,888			1,410,232,043
Redeemed		(9,305,861	)		(489,562,376	)		(19,652,428	)		(971,135,786	)
Net increase		4,779,659		$	234,149,226			23,519,042		$	1,165,143,938

37      OPPENHEIMER MAIN STREET FUND

NOTES TO FINANCIAL STATEMENTS Unaudited / Continued

6. Shares of Beneficial Interest (Continued)

	Six Months Ended February 28, 2018						Year Ended August 31, 2017
	Shares			Amount			Shares			Amount
Class B
Sold		7,982		$	402,651			42,232		$	1,938,888
Dividends and/or distributions reinvested		27,772			1,360,264			24,381			1,105,897
Acquisition—Note 10		—			—			139,958			6,738,964
Redeemed		(470,139	)		(23,923,177	)		(1,115,025	)		(52,116,284	)
Net decrease		(434,385	)	$	(22,160,262	)		(908,454	)	$	(42,332,535	)
Class C
Sold		780,223		$	38,913,666			2,152,450		$	99,460,275
Dividends and/or distributions reinvested		1,138,780			55,003,092			358,784			16,116,147
Acquisition—Note 10		—			—			1,532,129			73,051,894
Redeemed		(1,662,309	)		(82,889,764	)		(3,396,791	)		(159,650,103	)
Net increase		256,694		$	11,026,994			646,572		$	28,978,213
Class I
Sold		2,481,568		$	128,867,012			4,733,553		$	225,284,493
Dividends and/or distributions reinvested		1,094,260			55,085,076			483,270			22,544,516
Redeemed		(3,615,144	)		(188,587,496	)		(3,478,777	)		(168,804,623	)
Net increase (decrease)		(39,316	)	$	(4,635,408	)		1,738,046		$	79,024,386
Class R
Sold		787,719		$	40,936,704			1,150,451		$	55,572,177
Dividends and/or distributions reinvested		285,587			14,279,355			81,411			3,778,263
Acquisition—Note 10		—			—			358,243			17,672,147
Redeemed		(518,118	)		(26,763,700	)		(816,567	)		(39,302,261	)
Net increase		555,188		$	28,452,359			773,538		$	37,720,326
Class Y
Sold		2,436,771		$	127,094,469			7,170,469		$	350,686,799
Dividends and/or distributions reinvested		1,138,089			57,393,814			441,781			20,644,447
Acquisition—Note 10		—			—			424,922			21,135,599
Redeemed		(2,147,893	)		(112,122,577	)		(6,806,576	)		(334,994,083	)
Net increase		1,426,967		$	72,365,706			1,230,596		$	57,472,762

7. Purchases and Sales of Securities

The aggregate cost of purchases and proceeds from sales of securities, other than short-term obligations and investments in IGMMF, for the reporting period were as follows:

	Purchases		Sales
Investment securities	$	2,204,405,907	$	2,663,013,572

8. Fees and Other Transactions with Affiliates

Management Fees. Under the investment advisory agreement, the Fund pays the Manager

38      OPPENHEIMER MAIN STREET FUND

8. Fees and Other Transactions with Affiliates (Continued)

a management fee based on the daily net assets of the Fund at an annual rate as shown in the following table:

Fee Schedule
Up to $200 million	0.65%
Next $150 million	0.60
Next $150 million	0.55
Next $9.5 billion	0.45
Over $10 billion	0.43

The Fund’s effective management fee for the reporting period was 0.46% of average annual net assets before any applicable waivers.

Sub-Adviser Fees. The Manager has retained the Sub-Adviser to provide the day-to-day portfolio management of the Fund. Under the Sub-Advisory Agreement, the Manager pays the Sub-Adviser an annual fee in monthly installments, equal to a percentage of the investment management fee collected by the Manager from the Fund, which shall be calculated after any investment management fee waivers. The fee paid to the Sub-Adviser is paid by the Manager, not by the Fund.

Transfer Agent Fees. OFI Global (the “Transfer Agent”) serves as the transfer and shareholder servicing agent for the Fund. The Fund pays the Transfer Agent a fee based on annual net assets, which shall be calculated after any applicable fee waivers. Fees incurred and average net assets for each class with respect to these services are detailed in the Statement of Operations and Financial Highlights, respectively.

Sub-Transfer Agent Fees. The Transfer Agent has retained Shareholder Services, Inc., a wholly-owned subsidiary of OFI (the “Sub-Transfer Agent”), to provide the day-to-day transfer agent and shareholder servicing of the Fund. Under the Sub-Transfer Agency Agreement, the Transfer Agent pays the Sub-Transfer Agent an annual fee in monthly installments, equal to a percentage of the transfer agent fee collected by the Transfer Agent from the Fund, which shall be calculated after any applicable fee waivers. The fee paid to the Sub-Transfer Agent is paid by the Transfer Agent, not by the Fund.

Trustees’ Compensation. The Fund’s Board of Trustees (“Board”) has adopted a compensation deferral plan for Independent Trustees that enables Trustees to elect to defer receipt of all or a portion of the annual compensation they are entitled to receive from the Fund. For purposes of determining the amount owed to the Trustees under the plan, deferred amounts are treated as though equal dollar amounts had been invested in shares of the Fund or in other Oppenheimer funds selected by the Trustees. The Fund purchases shares of the funds selected for deferral by the Trustees in amounts equal to his or her deemed investment, resulting in a Fund asset equal to the deferred compensation liability. Such assets are included as a component of “Other” within the asset section of the Statement of Assets and Liabilities. Deferral of Trustees’ fees under the plan will not affect the net assets of the Fund and will not

39      OPPENHEIMER MAIN STREET FUND

NOTES TO FINANCIAL STATEMENTS Unaudited / Continued

8. Fees and Other Transactions with Affiliates (Continued)

materially affect the Fund’s assets, liabilities or net investment income per share. Amounts will be deferred until distributed in accordance with the compensation deferral plan.

Distribution and Service Plan (12b-1) Fees. Under its General Distributor’s Agreement with the Fund, OppenheimerFunds Distributor, Inc. (the “Distributor”) acts as the Fund’s principal underwriter in the continuous public offering of the Fund’s classes of shares.

Service Plan for Class A Shares. The Fund has adopted a Service Plan (the “Plan”) for Class A shares pursuant to Rule 12b-1 under the 1940 Act. Under the Plan, the Fund reimburses the Distributor for a portion of its costs incurred for services provided to accounts that hold Class A shares. Reimbursement is made periodically at an annual rate of up to 0.25% of the daily net assets of Class A shares of the Fund. The Distributor currently uses all of those fees to pay dealers, brokers, banks and other financial institutions periodically for providing personal service and maintenance of accounts of their customers that hold Class A shares. Any unreimbursed expenses the Distributor incurs with respect to Class A shares in any fiscal year cannot be recovered in subsequent periods. Fees incurred by the Fund under the Plan are detailed in the Statement of Operations.

Distribution and Service Plans for Class B, Class C and Class R Shares. The Fund has adopted Distribution and Service Plans (the “Plans”) for Class B, Class C and Class R shares pursuant to Rule 12b-1 under the 1940 Act to compensate the Distributor for distributing those share classes, maintaining accounts and providing shareholder services. Under the Plans, the Fund pays the Distributor an annual asset-based sales charge of 0.75% on Class B and Class C shares’ daily net assets and 0.25% on Class R shares’ daily net assets. The Fund also pays a service fee under the Plans at an annual rate of 0.25% of daily net assets. The Plans continue in effect from year to year only if the Fund’s Board of Trustees votes annually to approve their continuance at an in person meeting called for that purpose. Fees incurred by the Fund under the Plans are detailed in the Statement of Operations.

Sales Charges. Front-end sales charges and CDSC do not represent expenses of the Fund. They are deducted from the proceeds of sales of Fund shares prior to investment or from redemption proceeds prior to remittance, as applicable. The sales charges retained by the Distributor from the sale of shares and the CDSC retained by the Distributor on the redemption of shares is shown in the following table for the period indicated.

Six Months Ended	Class A Front-End Sales Charges Retained by Distributor		Class A Contingent Deferred Sales Charges Retained by Distributor		Class B Contingent Deferred Sales Charges Retained by Distributor		Class C Contingent Deferred Sales Charges Retained by Distributor		Class R Contingent Deferred Sales Charges Retained by Distributor
February 28, 2018		$623,601		$4,061		$5,350		$19,365		$—

Waivers and Reimbursements of Expenses. Effective for the period January 1, 2017

40      OPPENHEIMER MAIN STREET FUND

8. Fees and Other Transactions with Affiliates (Continued)

through December 31, 2017, the Transfer Agent voluntarily waived and/or reimbursed Fund expenses in an amount equal to 0.015% of average annual net assets for Classes A, B, C, I, R and Y.

During the reporting period, the Transfer Agent waived fees and/or reimbursed the Fund for transfer agent and shareholder servicing agent fees as follows:

Class A	$	376,216
Class B		1,392
Class C		41,642
Class R		10,114
Class Y		40,250

The Manager will waive fees and/or reimburse Fund expenses in an amount equal to the indirect management fees incurred through the Fund’s investment in IGMMF. During the reporting period, the Manager waived fees and/or reimbursed the Fund $94,507 for IGMMF management fees. This fee waiver and/or expense reimbursement may not be amended or withdrawn for one year from the date of the Fund’s prospectus, unless approved by the Board.

9. Borrowings and Other Financing

Joint Credit Facility. A number of mutual funds managed by the Manager participate in a $1.875 billion revolving credit facility (the “Facility”) intended to provide short-term financing, if necessary, subject to certain restrictions in connection with atypical redemption activity. Expenses and fees related to the Facility are paid by the participating funds and are disclosed separately or as other expenses on the Statement of Operations. The Fund did not utilize the Facility during the reporting period.

10. Acquisition of Oppenheimer Equity Fund

On March 17, 2017, the Fund acquired all of the net assets of Oppenheimer Equity Fund, pursuant to an Agreement and Plan of Reorganization approved by the Fund’s Board. The exchange qualified as a tax-free reorganization for federal income tax purposes. The purpose of this acquisition is to combine two funds with substantially similar investment objectives, strategies and risks to allow shareholders to benefit from greater asset growth potential, as well as lowered total expenses.

Details of the merger are shown in the following table:

41      OPPENHEIMER MAIN STREET FUND

NOTES TO FINANCIAL STATEMENTS Unaudited / Continued

10. Acquisition of Oppenheimer Equity Fund (Continued)

	Exchange Ratio to One Share of the Oppenheimer Equity Fund		Shares of Beneficial Interest Issued by the Fund		Value of Issued Shares of Beneficial Interest		Combined Net Assets on March 17, 20171
Class A		0.260382409		28,125,888		$1,410,232,043		$7,417,357,707
Class B		0.245447207		139,958		6,738,964		56,005,045
Class C		0.247985256		1,532,129		73,051,894		847,221,021
Class I		—		—		—		731,453,131
Class R		0.258994709		358,243		17,672,147		170,484,781
Class Y		0.262396643		424,922		$21,135,599		733,181,281

1. The net assets acquired included net unrealized appreciation of $326,717,562 and no capital loss carryforward.

Had the merger occurred at the beginning of the reporting period, the Fund’s Statement of Operations would have been adjusted to the following amounts (unaudited):

Net investment income	$	98,390,021
Net gain on investments		1,365,268,561
Net increase in net assets resulting from operations		1,463,658,582

For financial reporting purposes, assets received and shares issued by the Fund were recorded at fair value; however, the tax cost basis of the investments received from Oppenheimer Equity Fund were carried forward to align ongoing reporting of the Fund’s realized and unrealized gains and losses with amounts distributable to shareholders for tax purposes.

Because the combined investment portfolios have been managed as a single integrated portfolio since the acquisition was completed, it is not practicable to separate the amounts of revenue and earnings of Oppenheimer Equity Fund that have been included in the Fund’s Statement of Operations since March 17, 2017.

42      OPPENHEIMER MAIN STREET FUND

PORTFOLIO PROXY VOTING POLICIES AND GUIDELINES;

UPDATES TO STATEMENT OF INVESTMENTS Unaudited

The Fund has adopted Portfolio Proxy Voting Policies and Guidelines under which the Fund votes proxies relating to securities (“portfolio proxies”) held by the Fund. A description of the Fund’s Portfolio Proxy Voting Policies and Guidelines is available (i) without charge, upon request, by calling the Fund toll-free at 1.800.CALL OPP (225.5677), (ii) on the Fund’s website at www.oppenheimerfunds.com, and (iii) on the SEC’s website at www.sec.gov. In addition, the Fund is required to file Form N-PX, with its complete proxy voting record for the 12 months ended June 30th, no later than August 31st of each year. The Fund’s voting record is available (i) without charge, upon request, by calling the Fund toll-free at 1.800.CALL OPP (225.5677), and (ii) in the Form N-PX filing on the SEC’s website at www.sec.gov.

The Fund files its complete schedule of portfolio holdings with the SEC for the first quarter and the third quarter of each fiscal year on Form N-Q. The Fund’s Form N-Q filings are available on the SEC’s website at www.sec.gov. Those forms may be reviewed and copied at the SEC’s Public Reference Room in Washington, D.C. Information on the operation of the Public Reference Room may be obtained by calling 1-800-SEC-0330.

Householding—Delivery of Shareholder Documents

This is to inform you about OppenheimerFunds’ “householding” policy. If more than one member of your household maintains an account in a particular fund, OppenheimerFunds will mail only one copy of the fund’s prospectus (or, if available, the fund’s summary prospectus), annual and semiannual report and privacy policy. The consolidation of these mailings, called householding, benefits your fund through reduced mailing expense, and benefits you by reducing the volume of mail you receive from OppenheimerFunds. Householding does not affect the delivery of your account statements.

Please note that we will continue to household these mailings for as long as you remain an OppenheimerFunds shareholder, unless you request otherwise. If you prefer to receive multiple copies of these materials, please call us at 1.800.CALL-OPP (225-5677). You may also notify us in writing or via email. We will begin sending you individual copies of the prospectus (or, if available, the summary prospectus), reports and privacy policy within 30 days of receiving your request to stop householding.

43      OPPENHEIMER MAIN STREET FUND

DISTRIBUTION SOURCES Unaudited

For any distribution that took place over the last six months of the Fund’s reporting period, the table below details on a per-share basis the percentage of the Fund’s total distribution payment amount that was derived from the following sources: net income, net profit from the sale of securities, and other capital sources. Other capital sources represent a return of capital. A return of capital may occur, for example, when some or all of the money that you invested in the Fund is paid back to you. A return of capital distribution does not necessarily reflect the Fund’s investment performance and should not be confused with “yield” or “income.” You should not draw any conclusions about each Fund’s investment performance from the amounts of these distributions. This information is based upon income and capital gains using generally accepted accounting principles as of the date of each distribution. For certain securities, such as Master Limited Partnerships (“MLPs”) and Real Estate Investment Trusts (“REITs”), the percentages attributed to each category (net income, net profit from sale and other capital sources) are estimated using historical information because the character of the amounts received from the MLPs and REITs in which the fund invests is unknown until after the end of the calendar year. Because the Fund is actively managed, the relative amount of the Fund’s total distributions derived from various sources over the calendar year may change. Please note that this information should not be used for tax reporting purposes as the tax character of distributable income may differ from the amounts used for this notification. You will receive IRS tax forms in the first quarter of each calendar year detailing the actual amount of the taxable and non-taxable portion of distributions paid to you during the tax year.

For the most current information, please go to oppenheimerfunds.com. Select your Fund, and scroll down to the `Dividends’ table under `Analytics’. The Fund’s latest distribution information will be followed by the sources of any distribution, updated daily.

Fund Name	Pay Date		Net Income		Net Profit from Sale		Other Capital  Sources
Oppenheimer Main Street Fund		12/8/17		13.7%		85.9%		0.4%

44      OPPENHEIMER MAIN STREET FUND

OPPENHEIMER MAIN STREET FUND^®

Trustees and Officers	Robert J. Malone, Chairman of the Board of Trustees and Trustee
	Andrew J. Donohue, Trustee
	Richard F. Grabish, Trustee
	Beverly L. Hamilton, Trustee
	Victoria J. Herget, Trustee
	F. William Marshall, Jr., Trustee
	Karen L. Stuckey, Trustee
	James D. Vaughn, Trustee
	Arthur P. Steinmetz, Trustee, President and Principal Executive Officer
	Manind Govil, Vice President
	Benjamin Ram, Vice President
	Paul Larson, Vice President
	Cynthia Lo Bessette, Secretary and Chief Legal Officer
	Jennifer Foxson, Vice President and Chief Business Officer
	Mary Ann Picciotto, Chief Compliance Officer and Chief Anti-Money Laundering Officer
	Brian S. Petersen, Treasurer and Principal Financial & Accounting Officer
Manager	OFI Global Asset Management, Inc.
Sub-Adviser	OppenheimerFunds, Inc.
Distributor	OppenheimerFunds Distributor, Inc.
Transfer and Shareholder	OFI Global Asset Management, Inc.
Servicing Agent
Sub-Transfer Agent	Shareholder Services, Inc.
	DBA OppenheimerFunds Services
Independent Registered	KPMG LLP
Public Accounting Firm
Legal Counsel	Ropes & Gray LLP
	The financial statements included herein have been taken from the records of the Fund without examination of those records by the independent registered public accounting firm.

^© 2018 OppenheimerFunds, Inc. All rights reserved.

45      OPPENHEIMER MAIN STREET FUND

PRIVACY NOTICE

As an Oppenheimer fund shareholder, you are entitled to know how we protect your personal information and how we limit its disclosure.

Information Sources

We obtain non-public personal information about our shareholders from the following sources:

· Applications or other forms.

· When you create a user ID and password for online account access.

· When you enroll in eDocs Direct,^SM our electronic document delivery service.

· Your transactions with us, our affiliates or others.

· Technologies on our website, including: “cookies” and web beacons, which are used to collect data on the pages you visit and the features you use.

If you visit oppenheimerfunds.com and do not log on to the secure account information areas, we do not obtain any personal information about you. When you do log on to a secure area, we do obtain your user ID and password to identify you. We also use this information to provide you with products and services you have requested, to inform you about products and services that you may be interested in and assist you in other ways.

We do not collect personal information through our website unless you willingly provide it to us, either directly by email or in those areas of the website that request information. In order to update your personal information (including your mailing address, email address and phone number) you must first log on and visit your user profile.

If you have set your browser to warn you before accepting cookies, you will receive the warning message with each cookie. You can refuse cookies by turning them off in your browser. However, doing so may limit your access to certain sections of our website.

We use cookies to help us improve and manage our website. For example, cookies help us recognize new versus repeat visitors to the site, track the pages visited, and enable some special features on the website. This data helps us provide better service for our website visitors.

Protection of Information

We do not disclose any non-public personal information (such as names on a customer list) about current or former customers to anyone, except as permitted by law.

Disclosure of Information

Copies of confirmations, account statements and other documents reporting activity in your fund accounts are made available to your financial advisor (as designated by you). We may also use details about you and your investments to help us, our financial service affiliates, or firms that jointly market their financial products and services with ours, to better serve your investment needs or suggest educational material that may be of interest to you. If this requires us to provide you with an opportunity to “opt in” or “opt out” of such information sharing with a firm not affiliated with us, you will receive notification on how to do so, before any such sharing takes place.

Right of Refusal

We will not disclose your personal information to unaffiliated third parties (except as permitted by law), unless we first offer you a reasonable opportunity to refuse or “opt out” of such disclosure.

46      OPPENHEIMER MAIN STREET FUND

Internet Security and Encryption

In general, the email services provided by our website are encrypted and provide a secure and private means of communication with us. To protect your own privacy, confidential and/ or personal information should only be communicated via email when you are advised that you are using a secure website.

As a security measure, we do not include personal or account information in non-secure emails, and we advise you not to send such information to us in non-secure emails. Instead, you may take advantage of the secure features of our website to encrypt your email correspondence. To do this, you will need to use a browser that supports Secure Sockets Layer (SSL) protocol.

· All transactions conducted via our websites, including redemptions, exchanges and purchases, are secured by the highest encryption standards available. SSL is used to establish a secure connection between your PC and OppenheimerFunds’ server. It transmits information in an encrypted and scrambled format.

· Encryption is achieved through an electronic scrambling technology that uses a “key” to code and then decode the data. Encryption acts like the cable converter box you may have on your television set. It scrambles data with a secret code so that no one can make sense of it while it is being transmitted. When the data reaches its destination, the same software unscrambles the data.

· You can exit the secure area by closing your browser or, for added security, you can use the Log Out button before you close your browser.

Other Security Measures

We maintain physical, electronic and procedural safeguards to protect your personal account information. Our employees and agents have access to that information only so that they may offer you products or provide services, for example, when responding to your account questions.

How You Can Help

You can also do your part to keep your account information private and to prevent unauthorized transactions. If you obtain a user ID and password for your account, safeguard that information. Strengthening your online credentials–your online security profile–typically your user name, password, and security questions and answers, can be one of your most important lines of defense on the Internet. For additional information on how you can help prevent identity theft, visit https://www. oppenheimerfunds.com/security.

Who We Are

This joint notice describes the privacy policies of the Oppenheimer funds, OppenheimerFunds, Inc., each of its investment adviser subsidiaries, OppenheimerFunds Distributor, Inc. and OFI Global Trust Co. It applies to all Oppenheimer fund accounts you presently have, or may open in the future, using your Social Security number—whether or not you remain a shareholder of our funds. This notice was last updated as of November 2017. In the event it is updated or changed, we will post an updated notice on our website at oppenheimerfunds.com. If you have any questions about this privacy policy, email us by clicking on the Contact Us section of our website at oppenheimerfunds.com, write to us at P.O. Box 5270, Denver, CO 80217-5270, or call us at 800 CALL OPP (225 5677).

47      OPPENHEIMER MAIN STREET FUND

	OppenheimerFunds® The Right Way to Invest
	Visit us at oppenheimerfunds.com for 24-hr access to account information and transactions or call us at 800.CALL OPP (800.225.5677) for 24-hr automated information and automated transactions. Representatives also available Mon–Fri 8am-8pm ET.
Visit Us oppenheimerfunds.com
Call Us 800 225 5677
Follow Us
	Oppenheimer funds are distributed by OppenheimerFunds Distributor, Inc. 225 Liberty Street, New York, NY 10281-1008 © 2018 OppenheimerFunds Distributor, Inc. All rights reserved. RS0700.001.0218 April 24, 2018

Item 2. Code of Ethics.

Not applicable to semiannual reports.

Item 3. Audit Committee Financial Expert.

Not applicable to semiannual reports.

Item 4. Principal Accountant Fees and Services.

Not applicable to semiannual reports.

Item 5. Audit Committee of Listed Registrants

Not applicable.

Item 6. Schedule of Investments.

a) Not applicable. The complete schedule of investments is included in Item 1 of this Form N-CSR.

b) Not applicable.

Item 7. Disclosure of Proxy Voting Policies and Procedures for Closed-End Management Investment Companies.

Not applicable.

Item 8. Portfolio Managers of Closed-End Management Investment Companies.

Not applicable.

Item 9. Purchases of Equity Securities by Closed-End Management Investment Company and Affiliated Purchasers.

Not applicable.

Item 10. Submission of Matters to a Vote of Security Holders.

The Fund’s Governance Committee Provisions with Respect to Nominations of Directors/Trustees to the Respective Boards

None

Item 11. Controls and Procedures.

Based on their evaluation of the registrant’s disclosure controls and procedures (as defined in rule 30a-3(c) under the Investment Company Act of 1940 (17 CFR 270.30a-3(c)) as of 2/28/2018, the registrant’s principal executive officer and principal financial officer found the registrant’s disclosure controls and procedures to provide reasonable assurances that information required to be disclosed by the registrant in the reports that it files under the Securities Exchange Act of 1934 (a) is accumulated and communicated to registrant’s management, including its principal executive officer and principal financial officer, to allow timely decisions regarding required disclosure, and (b) is recorded, processed, summarized and reported, within the time

periods specified in the rules and forms adopted by the U.S. Securities and Exchange Commission.

There have been no changes in the registrant’s internal controls over financial reporting that occurred during the registrant’s second fiscal quarter of the period covered by this report that have materially affected, or are reasonably likely to materially affect, the registrant’s internal control over financial reporting.

Item 12. Disclosure of Securities Lending Activities for Closed-End Management Investment Companies.

Not applicable.

Item 13. Exhibits.

(a) (1) Exhibit attached hereto.

(2) Exhibits attached hereto.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Oppenheimer Main Street Funds

By:	/s/ Arthur P. Steinmetz
	Arthur P. Steinmetz
	Principal Executive Officer
Date:	4/20/2018

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

By:	/s/ Arthur P. Steinmetz
	Arthur P. Steinmetz
	Principal Executive Officer
Date:	4/20/2018

By:	/s/ Brian S. Petersen
	Brian S. Petersen
	Principal Financial Officer
Date:	4/20/2018

EX-99.CERT

Exhibit 99.CERT

Section 302 Certifications

CERTIFICATIONS

I, Arthur P. Steinmetz, certify that:

1. I have reviewed this report on Form N-CSR of Oppenheimer Main Street Funds;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations, changes in net assets, and cash flows (if the financial statements are required to include a statement of cash flows) of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940) and internal control over financial reporting (as defined in Rule 30a-3(d) under the Investment Company Act of 1940) for the registrant and have:

(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of a date within 90 days prior to the filing date of this report based on such evaluation; and

(d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the second fiscal quarter of the period covered by this report that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer and I have disclosed to the registrant’s auditors and the audit committee of the registrant’s board of Trustees (or persons performing the equivalent functions):

(a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize, and report financial information; and

(b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: 4/20/2018

/s/ Arthur P. Steinmetz

Arthur P. Steinmetz

Principal Executive Officer

Exhibit 99.CERT

Section 302 Certifications

CERTIFICATIONS

I, Brian S. Petersen, certify that:

1. I have reviewed this report on Form N-CSR of Oppenheimer Main Street Funds;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations, changes in net assets, and cash flows (if the financial statements are required to include a statement of cash flows) of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940) and internal control over financial reporting (as defined in Rule 30a-3(d) under the Investment Company Act of 1940) for the registrant and have:

(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

(b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of a date within 90 days prior to the filing date of this report based on such evaluation; and

(d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the second fiscal quarter of the period covered by this report that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer and I have disclosed to the registrant’s auditors and the audit committee of the registrant’s board of Trustees (or persons performing the equivalent functions):

(a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize, and report financial information; and

(b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: 4/20/2018

/s/ Brian S. Petersen

Brian S. Petersen

Principal Financial Officer

EX-99.906CERT

EX-99.906CERT

Section 906 Certifications

CERTIFICATION PURSUANT TO 18 U.S.C SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

Arthur P. Steinmetz, Principal Executive Officer, and Brian S. Petersen, Principal Financial Officer, of Oppenheimer Main Street Funds (the “Registrant”), each certify to the best of his knowledge that:

1. The Registrant’s periodic report on Form N-CSR for the period ended 2/28/2018 (the “Form N-CSR”) fully complies with the requirements of Section 15(d) of the Securities Exchange Act of 1934, as amended; and

2. The information contained in the Form N-CSR fairly presents, in all material respects, the financial condition and results of operations of the Registrant. This certification is being furnished to the Commission solely pursuant to 18 U.S.C. § 1350 and is not being filed as part of the Form N-CSR filed with the Commission.

Principal Executive Officer	Principal Financial Officer
Oppenheimer Main Street Funds	Oppenheimer Main Street Funds

/s/ Arthur P. Steinmetz	/s/ Brian S. Petersen
Arthur P. Steinmetz	Brian S. Petersen
Date: 4/20/2018	Date: 4/20/2018