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 811-21888

Oppenheimer Institutional Government Money Market Fund

(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: May 31

Date of reporting period: 5/31/2018

Item 1. Reports to Stockholders.

Table of Contents
Fund Performance Discussion	3
Portfolio Allocation	5
Fund Expenses	7
Statement of Investments	9
Statement of Assets and Liabilities	15
Statement of Operations	16
Statements of Changes in Net Assets	17
Financial Highlights	18
Notes to Financial Statements	21
Report of Independent Registered Public Accounting Firm	31
Federal Income Tax Information	32
Portfolio Proxy Voting Policies and Guidelines; Updates to Statement of Investments	33
Distribution Sources	34
Trustees and Officers	35
Privacy Notice	42

2      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

Fund Performance Discussion

Throughout the reporting period, the Fund continued to offer very strong liquidity and a stable $1.00 net asset value (NAV), while providing competitive income. At its March meeting, the Federal Open Market Committee (FOMC) voted to lift the Federal Funds Rate for the first time in 2018, to a range of 1.50% to 1.75%, completing its sixth hike in this cycle. The Fund continued to benefit from these rate hikes, with ongoing reinvestment at higher rates. With the added expectation for further hikes this year, we believe the Fund’s yield forecast remains optimistic.

MARKET OVERVIEW

In November of 2017, it was announced that Jerome Powell would become the 16th Chair of the Federal Reserve (the “Fed”). Many market participants believe his appointment by President Trump will allow for a continuation of policy – a slow and steady rise in the Fed Funds Rate. Mr. Powell has served on the Federal Reserve Board of Governors since 2012 and during this tenure has voted in harmony with the FOMC statements under both Yellen and Bernanke. In addition to a new Fed Chair, there have been five open seats on the FOMC.

Current broader market and FOMC consensus is for three hikes in 2018. We estimate the most likely scenario includes a hike at each of the June and September meetings. Should the markets remain stable and steady, many on the street are forecasting four hikes in 2018. The more conservative consensus view puts the Fed Funds Rate in the 2.00% to 2.25% range at year end. Coupled with these hikes, the Fed plans to shrink its balance sheet from

$4.5 trillion, a move it started in October 2017. While the Fed has not indicated a balance sheet level it intends to hit, it has denoted the holdings will not return to pre-recession levels (less than $1 trillion).

Another area of continued interest is in Treasury bill supply. Once the debt ceiling issue was resolved, the Treasury restocked its cash balances in the first quarter of 2018 with record Treasury bill issuance. This anticipated increase in supply had a favorable impact on money market yields. In April 2018, net Treasury bill supply was negative and some are predicting issuance through year-end to be flat. We continue to keep a watchful eye on the prospects of the U.S. Treasury issuing a 2-month Treasury bill. While this has been in the works for some time now, expectations are for a September issuance.

Finally, the market witnessed a large spread difference in the 3-month London interbank offered rate and Overnight Index Swap rate

3      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

in the month of April.¹ The noise brought back memories of previous spikes, notably the 2008 financial crisis and the European debt crisis. However, this time around, the increase was not due to any credit concerns but rather the excess Treasury supply mentioned above and the repatriation of overseas cash. With the excess of Treasury bill supply, coupled with the Fed rate hikes, we continue to welcome higher rates and look forward to passing those on to our investors.

FUND REVIEW

The Fund’s weighted average maturity throughout the reporting period averaged 38 days with a range of 28-48 days. We continue to layer in floating-rate securities when we believe they are fairly priced. Supply continues to be available, notably in Federal Home Loan Bank paper. We are heavily weighted in government repurchase agreements and will occasionally add some long dated fixed

paper to the portfolio. We remain confident the Fund is well positioned should the Fed continue its gradual, upward trajectory on the Fed Funds Rate.

STRATEGY & OUTLOOK

Our strategy continues to incorporate select incremental investing as we seek to provide shareholders stable and steady value. We intend to remain active in the auction market, with most of that weight going to fixed-rate instruments with durations of three months or less. When pricing allows, we will continue to layer in one- and three-month floating rate securities. Our outlook is for continued rate hikes in 2018, and our investment strategy is in line with Fed’s dot plot for more hikes this year. We believe the Fund is well-positioned to take advantage of these higher rates as long as the Fed continues on a path of slow and steady hikes.

	Christopher Proctor, CFA
	Portfolio Manager

	Adam S. Wilde, CFA
	Portfolio Manager

1. The London InterBank Offered Rate (LIBOR) is the average interest rate estimated by leading banks in London that they would be charged if borrowing from other banks. It is a primary benchmark for short- term interest rates around the world. The Overnight Index Swap rate is the difference between the overnight lending rates set by central banks and the three-month Libor. The Overnight Index Swap rate tracks the relationship between an expected three-month Fed funds rate and three-month Libor.

4      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

Portfolio Allocation

U.S. Government Agencies	56.0%
Repurchase Agreements	42.9
U.S. Government Obligations	0.7
Investment Companies	0.4

Portfolio holdings and allocations are subject to change. Percentages are as of May 31, 2018, and are based on the total market value of investments.

Performance

CURRENT YIELD

For the 7-Day Period Ended May 31, 2018

	With Compounding			Without Compounding
Class E (IOEXX)		1.72	%		1.71	%
Class L (IOLXX)		1.65			1.63
Class P (IOPXX)		1.65			1.64

CURRENT YIELD

For the Year Ended May 31, 2018

	With Compounding			Without Compounding
Class E (IOEXX)		1.18	%		1.17	%
Class L (IOLXX)		1.12			1.12
Class P (IOPXX)		1.12			1.11

Compounded yields assume reinvestment of dividends. The seven-day yield without compounding is an annualized average daily yield of the Fund for the most recent seven days. The compounded seven-day average yield for 365 days is offered as a comparison to a savings account’s compounded interest rate. Unlike an investment in the Fund, the FDIC generally insures deposits in savings accounts.

Performance data quoted represents past performance, which does not guarantee future results. Yields include dividends in a hypothetical investment for the periods shown. Current performance may be lower or higher than the performance quoted. For performance data current to the most recent month-end, visit oppenheimerfunds.com or call 1.800.CALL OPP (225.5677). The yields take into account voluntary fee waivers and/or expense reimbursements, without which yields would have been lower. Some of these undertakings may be modified or terminated at any time, as indicated in the Fund’s prospectus. The Fund’s performance shown does not reflect the deduction of income taxes on an individual’s investment. Taxes may reduce your actual investment returns on income paid by the Fund. There is no guarantee that the Fund will maintain a positive yield.

5      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

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.

You could lose money by investing in the Fund. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Fund’s sponsor has no legal obligation to provide financial support to the Fund, and you should not expect that the sponsor will provide financial support to the Fund at any time.

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 May 31, 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.

6      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET 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 May 31, 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 May 31, 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.

7      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

Actual	Beginning   Account   Value   December 1, 2017		Ending     Account     Value     May 31, 2018		Expenses         Paid During         6 Months Ended         May 31, 2018
Class E	$	1,000.00	$	1,007.00	$	0.50
Class L		1,000.00		1,006.80		0.80
Class P		1,000.00		1,006.70		0.90
Hypothetical
(5% return before expenses)
Class E		1,000.00		1,024.43		0.50
Class L		1,000.00		1,024.13		0.81
Class P		1,000.00		1,024.03		0.91

Expenses are equal to the Fund’s annualized expense ratio for that class, multiplied by the average account value over the period, multiplied by 182/365 (to reflect the one-half year period). Those annualized expense ratios, excluding indirect expenses from affiliated funds, based on the 6-month period ended May 31, 2018 are as follows:

Class	Expense Ratios
Class E		0.10	%
Class L		0.16
Class P		0.18

The expense ratios reflect voluntary and/or contractual waivers and/or reimbursements of expenses by the Fund’s Distributor. 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.

8      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

STATEMENT OF INVESTMENTS May 31, 2018

	Maturity Date*		Final Legal Maturity Date**		Principal Amount		Value
U.S. Government Agencies—56.2%
Federal Agricultural Mortgage Corp., 1.812%
[US0001M-10.5]1		6/4/18		9/4/18	$	35,000,000	$	35,000,000
Federal Farm Credit Bank:
1.264%2		6/7/18		6/7/18		5,000,000		4,998,958
1.265%2		6/27/18		6/27/18		10,000,000		9,990,972
1.272%2		7/16/18		7/16/18		9,000,000		8,985,875
1.603%2		7/23/18		7/23/18		800,000		798,163
1.629%2		6/22/18		6/22/18		15,000,000		14,985,825
1.63% [FCPR DLY-312]1		6/1/18		1/2/19		35,000,000		35,000,000
1.68% [FCPR DLY-307]1		6/1/18		2/20/19		73,000,000		72,996,506
1.801%2		12/12/18		12/12/18		10,000,000		9,904,616
1.808% [US0001M-11]1		6/12/18		3/12/19		74,000,000		73,998,273
1.815%2		11/1/18		11/1/18		42,000,000		41,680,485
1.838% [US0001M-13]1		6/27/18		3/27/19		55,000,000		54,989,068
1.843% [US0001M-8.5]1		6/9/18		7/9/19		75,000,000		74,992,807
1.848% [US0001M-8]1		6/9/18		11/9/18		15,000,000		15,001,290
1.85%2		12/10/18		12/10/18		14,000,000		13,864,107
1.871%2		12/17/18		12/17/18		16,000,000		15,837,262
1.893% [US0001M-7.5]1		6/29/18		10/29/18		30,000,000		29,999,311
1.903% [US0001M-6.5]1		6/28/18		3/28/19		75,000,000		75,000,000
1.969%2		2/5/19		2/5/19		5,000,000		4,933,254
2.035% [US0003M-26]1		6/28/18		9/28/18		10,000,000		9,997,405
2.078% [US0001M+13]1		6/19/18		7/19/18		10,000,000		10,003,341
2.078% [US0003M-23]1		7/3/18		4/3/19		11,600,000		11,601,162
2.081% [US0001M+12]1		6/23/18		11/23/18		10,000,000		10,011,343
2.186%2		4/3/19		4/3/19		36,000,000		35,345,160
2.187%2		4/9/19		4/9/19		50,000,000		49,072,667
2.194%2		1/17/19		1/17/19		5,000,000		4,931,000
2.198%2		4/15/19		4/15/19		20,000,000		19,620,167
2.252%2		2/21/19		2/21/19		15,000,000		14,755,979
2.265%2		3/11/19		3/11/19		7,500,000		7,369,113
2.276%2		3/19/19		3/19/19		7,500,000		7,364,806
2.345% [US0003M-1]1		7/19/18		10/19/18		24,200,000		24,216,644
Federal Home Loan Bank:
0.875%		6/29/18		6/29/18		18,990,000		18,983,045
0.875%		8/8/18		8/8/18		5,000,000		4,990,699
1.125%		9/14/18		9/14/18		2,000,000		1,996,608
1.187%		8/7/18		8/7/18		37,600,000		37,554,141
1.25%		1/16/19		1/16/19		25,000,000		24,893,552
1.257%		6/8/18		6/8/18		20,500,000		20,499,427
1.266%2		7/27/18		7/27/18		6,000,000		5,988,333
1.274%		7/24/18		7/24/18		33,000,000		32,998,877
1.281%		7/27/18		7/27/18		27,755,000		27,753,670
1.375%		3/18/19		3/18/19		27,215,000		27,044,532
1.50%		3/8/19		3/8/19		46,000,000		45,764,823
1.501%2		6/20/18		6/20/18		25,000,000		24,980,340
1.52%2		6/25/18		6/25/18		50,000,000		49,949,667

9      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

STATEMENT OF INVESTMENTS Continued

	Maturity Date*		Final Legal Maturity Date**		Principal Amount		Value
U.S. Government Agencies (Continued)
Federal Home Loan Bank: (Continued)
1.532%2		6/26/18		6/26/18	$	3,500,000	$	3,496,306
1.598%2		7/24/18		7/24/18		20,000,000		19,953,331
1.612%2		7/23/18		7/23/18		8,346,000		8,326,711
1.648%2		8/1/18		8/1/18		111,905,000		111,595,077
1.654%2		8/8/18		8/8/18		50,000,000		49,845,111
1.687%2		6/13/18		6/13/18		29,000,000		28,983,763
1.734%2		6/27/18		6/27/18		64,000,000		63,920,238
1.744%2		8/10/18		8/10/18		15,000,000		14,949,571
1.75%		12/14/18		12/14/18		72,055,000		72,016,134
1.751%2		8/3/18		8/3/18		97,000,000		96,704,810
1.769% [US0001M-14]1		6/2/18		1/2/19		18,000,000		18,000,000
1.777% [US0001M-13]1		6/1/18		8/30/18		53,000,000		53,000,000
1.787%2		7/13/18		7/13/18		65,194,000		65,058,652
1.793% [US0001M-13]1		6/6/18		9/6/18		78,000,000		77,991,343
1.797% [US0001M-11]1		6/1/18		2/1/19		36,000,000		36,000,000
1.797%2		6/15/18		6/15/18		18,000,000		17,987,477
1.809% [US0001M-11]1		6/15/18		12/14/18		55,000,000		55,000,000
1.818% [US0001M-13]1		6/20/18		7/20/18		73,000,000		73,005,526
1.818% [US0001M-13]1		6/20/18		8/20/18		37,000,000		37,000,000
1.819% [US0001M-11]1		6/11/18		10/11/18		8,000,000		8,000,195
1.828% [US0001M-9]1		6/14/18		1/14/19		21,000,000		21,004,939
1.83% [US0001M-13]1		6/25/18		7/25/18		35,000,000		35,000,000
1.83% [US0001M-13]1		6/25/18		2/25/19		57,000,000		57,001,781
1.83% [US0001M-13]1		6/25/18		1/25/19		35,000,000		35,000,000
1.833% [US0001M-9]1		6/6/18		4/5/19		36,000,000		36,000,000
1.833% [US0001M-13.5]1		6/27/18		12/27/18		35,000,000		35,002,214
1.833% [US0001M-8.5]1		6/13/18		3/13/19		30,300,000		30,306,315
1.838% [US0001M-11]1		6/21/18		12/21/18		18,000,000		18,000,000
1.839% [US0001M-9]1		6/11/18		1/11/19		50,000,000		50,010,616
1.84% [US0001M-12]1		6/25/18		3/25/19		55,000,000		55,000,000
1.843% [US0001M-22]1		6/22/18		2/22/19		117,000,000		116,998,413
1.843% [US0001M-11]1		6/22/18		4/22/19		75,000,000		74,988,172
1.845% [US0001M-11.5]1		6/25/18		10/25/18		35,000,000		35,000,000
1.846% [US0001M-11.5]1		6/23/18		8/23/18		35,000,000		35,000,000
1.852% [US0001M-13]1		6/1/18		3/1/19		18,000,000		18,000,000
1.853%2		7/11/18		7/11/18		37,000,000		36,924,026
1.858% [US0001M-9]1		6/21/18		6/21/19		12,810,000		12,803,711
1.863% [US0001M-10.5]1		6/26/18		5/24/19		37,000,000		37,000,000
1.863% [US0001M-10.5]1		6/28/18		5/28/19		53,000,000		52,998,322
1.865%2		7/12/18		7/12/18		37,000,000		36,921,622
1.868% [US0001M-10]1		6/27/18		12/27/18		34,000,000		33,997,709
1.868% [US0001M-8]1		6/20/18		3/20/19		46,000,000		45,995,676
1.874%2		7/18/18		7/18/18		37,000,000		36,909,717
1.875%		3/8/19		3/8/19		20,500,000		20,449,514
1.908% [US0001M-6]1		6/26/18		4/26/19		80,000,000		80,000,000
1.911% [US0003M-16]1		6/12/18		6/12/19		9,475,000		9,476,078

10      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

			Final Legal
	Maturity		Maturity		Principal
	Date*		Date**		Amount		Value
U.S. Government Agencies (Continued)
Federal Home Loan Bank: (Continued)
1.913%2		10/10/18		10/10/18	$	85,000,000	$	84,413,866
1.917% [US0003M-19]1		6/14/18		9/14/18		35,000,000		35,000,000
1.923%2		10/12/18		10/12/18		40,000,000		39,718,631
1.93%		8/31/18		8/31/18		30,000,000		29,854,324
1.934% [US0003M-40.5]1		7/30/18		1/30/19		75,000,000		75,000,000
1.99%2		10/17/18		10/17/18		75,000,000		74,433,625
1.991% [US0003M-34]1		7/9/18		4/9/19		37,000,000		37,000,000
2.00%		9/14/18		9/14/18		14,990,000		15,001,686
2.02%2		10/22/18		10/22/18		54,000,000		53,571,000
2.041% [US0003M-24.5]1		6/26/18		9/26/18		71,000,000		71,000,000
2.076%2		11/28/18		11/28/18		70,000,000		69,282,500
2.111% [US0003M-22]1		7/9/18		7/9/18		75,600,000		75,598,596
2.111% [US0003M-21]1		7/5/18		7/5/18		35,000,000		35,000,000
2.125%		4/18/19		4/18/19		7,250,000		7,244,772
2.166%2		3/28/19		3/28/19		24,000,000		23,575,999
Federal Home Loan Mortgage Corp.:
3.75%		3/27/19		3/27/19		16,137,000		16,342,062
4.875%		6/13/18		6/13/18		25,850,000		25,878,247
Federal National Mortgage Assn.:
1.00%		2/26/19		2/26/19		20,200,000		20,029,018
1.125%		12/14/18		12/14/18		35,015,000		34,880,383
1.203%		7/20/18		7/20/18		17,000,000		16,996,878
1.264%		7/27/18		7/27/18		12,725,000		12,714,954
Tennessee Valley Authority:
1.74%2		6/12/18		6/12/18		113,000,000		112,939,981
1.772%2		6/19/18		6/19/18		77,000,000		76,931,855
Total U.S. Government Agencies (Cost $4,129,674,720)								4,129,674,720
U.S. Government Obligations—0.7%
United States Treasury Bills, 1.965% (Cost $54,586,745)2		10/18/18		10/18/18		55,000,000		54,586,745
Repurchase Agreements—43.0%
Repurchase Agreements3 (Cost $3,162,000,000)						3,162,000,000		3,162,000,000
					Shares
Investment Companies—0.4%
Goldman Sachs Financial Square Government Fund, 1.65%4						29,754,986		29,754,986
JPMorgan U.S. Government Money Market Fund, 1.62%4						306,913		306,913
Total Investment Companies (Cost $30,061,899)								30,061,899
Total Investments, at Value (Cost $7,376,323,364)						100.3%		7,376,323,364
Net Other Assets (Liabilities)						(0.3)		(19,208,055	)
Net Assets						100.0%	$	7,357,115,309

11      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

STATEMENT OF INVESTMENTS Continued

Footnotes to Statement of Investments

Short-term notes and direct bank obligations are generally traded on a discount basis; the interest rate shown is the discount rate received by the Fund at the time of purchase. Other securities normally bear interest at the rates shown.

* The Maturity Date represents the date used to calculate the Fund’s weighted average maturity as determined under Rule 2a-7.

** If different from the Maturity Date, the Final Legal Maturity Date includes any maturity date extensions which may be affected at the option of the issuer or unconditional payments of principal by the issuer which may be affected at the option of the Fund, and represents the date used to calculate the Fund’s weighted average life as determined under Rule 2a-7.

1. Represents the current interest rate for a variable or increasing rate security, determined as [Referenced Rate + Basis-point spread].

2. Zero coupon bond reflects effective yield on the original acquisition date.

3. Repurchase agreements:

	Lending		Settlement		Maturity		Principal
Counterparty	Rate		Date		Date		Amount
Credit Agricole Corp. & Investment Bank		1.74%		5/14/18		6/13/18		$104,000,000
Credit Agricole Corp. & Investment Bank		1.74		5/11/18		6/11/18		65,000,000
Credit Agricole Corp. & Investment Bank		1.75		5/31/18		6/1/18		175,000,000
Credit Agricole Corp. & Investment Bank		1.76		5/31/18		6/1/18		303,500,000
Deusche Bank Securities, Inc.		1.74		5/16/18		6/15/18		75,000,000
Deusche Bank Securities, Inc.		1.79		5/31/18		6/1/18		169,400,000
INTL FCStone Financial, Inc.		1.72		5/29/18		6/5/18		135,000,000
INTL FCStone Financial, Inc.		1.72		5/30/18		6/6/18		60,000,000
RBC Dominion Securities, Inc.		1.75		5/31/18		6/1/18		421,800,000
Royal Bank of Canada		1.76		5/31/18		6/1/18		376,300,000
South Street Securities LLC		1.77		5/29/18		6/5/18		500,000,000
South Street Securities LLC		1.80		5/31/18		6/1/18		498,000,000
TD Securities (USA) LLC		1.76		5/31/18		6/7/18		145,000,000
TD Securities (USA) LLC		1.78		5/31/18		6/1/18		134,000,000

12      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

Footnotes to Statement of Investments (Continued)

Counterparty	Collateralized By	Collateral Received, at Valuea		Repurchase Agreements,at Value		Repurchase Agreement Proceeds to be Receiveda
Credit Agricole Corp. & Investment Bank	U.S. Government Agency Mortgages, 3.50%, 11/20/47		$(106,233,816)		$104,000,000		$104,150,800
Credit Agricole Corp. & Investment Bank	U.S. Government Agency Mortgages, 3.00%, 11/20/47		(66,399,340)		65,000,000		65,097,392
Credit Agricole Corp. & Investment Bank	U.S. Government Agency Mortgages, 3.50%-4.00%, 11/1/44-2/20/48		(178,508,677)		175,000,000		175,008,507
Credit Agricole Corp. & Investment Bank	U.S. Government Agency Mortgages, 1.75%-4.00%, 1/30/20-8/20/47		(309,585,135)		303,500,000		303,514,838
Deusche Bank Securities, Inc.	U.S. Government Agency Mortgages, 3.00%, 11/15/56		(82,563,801)		75,000,000		75,058,001
Deusche Bank Securities, Inc.	U.S. Government Agency Mortgages, 3.00%-3.50%, 4/15/45-1/15/56		(186,349,266)		169,400,000		169,408,423
INTL FCStone Financial, Inc.	U.S. Treasury Bills, 0.00%, 6/21/18-3/28/19; U.S. Treasury Bonds, 3.125%- 6.625%, 2/15/27-5/15/48; U.S. Treasury Nts., 0.125%- 2.875%, 7/31/18-5/15/28 and U.S. Government Agency Mortgages, 0.00%- 10.00%, 6/15/18-2/1/57		(139,102,513)		135,000,000		135,020,956
INTL FCStone Financial, Inc.	U.S. Treasury Bills, 0.00%, 6/14/18-7/26/18; U.S. Treasury Bonds, 3.125%- 3.75%, 11/15/43-8/15/44; U.S. Treasury Nts., 0.00%- 3.125%, 7/31/18-2/15/46 and U.S. Government Agency Mortgages, 0.00%- 7.50%, 6/25/18-2/1/57		(62,597,413)		60,000,000		60,013,009
RBC Dominion Securities, Inc.	U.S. Treasury Nts., 2.125%- 2.25%, 2/29/24-11/15/27 and U.S. Government Agency Mortgages, 3.00%- 5.00%, 8/1/40-11/20/47		(430,256,947)		421,800,000		421,820,536
Royal Bank of Canada	U.S. Government Agency Mortgages, 2.03%-4.50%, 2/1/27-5/1/48		(383,844,765)		376,300,000		376,318,397

13      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

STATEMENT OF INVESTMENTS Continued

Footnotes to Statement of Investments (Continued)

Counterparty	Collateralized By	Collateral Received, at Valuea	Repurchase Agreements, at Value		Repurchase Agreement Proceeds to be Receiveda
South Street Securities LLC	U.S. Treasury Nts., 0.50%-2.375%, 8/31/21-1/15/28 and U.S. Government Agency Mortgages, 2.003%-7.50%, 12/13/19-5/1/48	$(510,075,225)		$500,000,000	$500,073,750
South Street Securities LLC	U.S. Treasury Nts., 2.25%, 12/31/23-11/15/24 and U.S. Government Agency Mortgages, 1.125%-9.20%, 6/8/18-5/1/50	(507,985,398)		498,000,000	498,024,900
TD Securities (USA) LLC	U.S. Treasury Nts., 0.00%, 11/15/43 and U.S. Government Agency Mortgages, 3.50%, 7/1/46	(147,907,232)		145,000,000	145,007,090
TD Securities (USA) LLC	U.S. Treasury Nts., 0.00%-1.181%, 10/31/19-11/15/46 and U.S. Government Agency Mortgages, 0.00%-7.125%, 6/4/18-9/15/65	(136,687,171)		134,000,000	134,007,031
		$(3,248,096,699)	$	3,162,000,000	$3,162,523,630
a. Includes accrued interest. 4. Rate shown is the 7-day yield at period end.

Glossary:
Definitions
FCPR DLY	Federal Reserve Bank Prime Loan Rate US Daily
ICE LIBOR	Intercontinental Exchange London Interbank Offered Rate
US0001M	ICE LIBOR USD 1 Month
US0003M	ICE LIBOR USD 3 Month

See accompanying Notes to Financial Statements.

14      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

STATEMENT OF ASSETS AND LIABILITIES May 31, 2018

Assets
Investments, at value—see accompanying statement of investments:
Unaffiliated companies (cost $4,214,323,364)	$	4,214,323,364
Repurchase agreements (cost 3,162,000,000)		3,162,000,000
		7,376,323,364
Cash		540,179
Receivables and other assets:
Investments sold on a when-issued or delayed delivery basis		13,638,569
Interest and dividends		5,744,719
Shares of beneficial interest sold		367,055
Other		359,203
Total assets		7,396,973,089
Liabilities
Payables and other liabilities:
Investments purchased		29,854,324
Dividends		9,360,935
Trustees’ compensation		538,637
Shareholder communications		8,860
Distribution and service plan fees		166
Other		94,858
Total liabilities		39,857,780
Net Assets	$	7,357,115,309
Composition of Net Assets
Par value of shares of beneficial interest	$	7,357,472
Additional paid-in capital		7,350,128,484
Accumulated net investment loss		(329,224	)
Accumulated net realized loss on investments		(41,423	)
Net Assets	$	7,357,115,309
Net Asset Value Per Share
Class E Shares:
Net asset value and redemption price per share (based on net assets of $7,127,369,474 and 7,127,630,873 shares of beneficial interest outstanding)		$1.00
Class L Shares:
Net asset value and redemption price per share (based on net assets of $221,575,352 and 221,686,221 shares of beneficial interest outstanding)		$1.00
Class P Shares:
Net asset value and redemption price per share (based on net assets of $8,170,483 and 8,155,225 shares of beneficial interest outstanding)		$1.00
See accompanying Notes to Financial Statements.

15      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

STATEMENT OF

OPERATIONS For the Year Ended May 31, 2018

Investment Income
Interest	$	85,854,323
Dividends		816,863
Total investment income		86,671,186
Expenses
Management fees		6,709,388
Distribution and service plan fees — Class P		20,288
Transfer and shareholder servicing agent fees:
Class L		178,434
Class P		4,058
Shareholder communications — Class L		7,902
Trustees’ compensation		95,747
Custodian fees and expenses		42,037
Other		180,872
Total expenses		7,238,726
Less waivers and reimbursements of expenses		(19,140	)
Net expenses		7,219,586
Net Investment Income		79,451,600
Net Realized Loss on Investments		(34,738	)
Net Increase in Net Assets Resulting from Operations	$	79,416,862

See accompanying Notes to Financial Statements.

16      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

STATEMENTS OF CHANGES IN NET ASSETS

	Year Ended May 31, 2018			Year Ended May 31, 2017
Operations
Net investment income	$	79,451,600		$      32,110,382
Net realized gain (loss)		(34,738	)	74,703
Net increase in net assets resulting from operations		79,416,862		32,185,085
Dividends and/or Distributions to Shareholders
Dividends from net investment income:
Class E		(75,631,347	)	(28,584,118)
Class L		(3,701,843	)	(3,493,957)
Class P		(90,000	)	(33,170)
		(79,423,190	)	(32,111,245)
Beneficial Interest Transactions
Net increase (decrease) in net assets resulting from beneficial interest transactions:
Class E		1,087,769,065		(604,045,129)
Class L		(674,107,452	)	97,396,937
Class P		90,000		33,170
		413,751,613		(506,615,022)
Net Assets
Total increase (decrease)		413,745,285		(506,541,182)
Beginning of period		6,943,370,024		7,449,911,206
End of period (including accumulated net investment loss of $329,224 and $425,384, respectively)	$	7,357,115,309		$  6,943,370,024

See accompanying Notes to Financial Statements.

17      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

FINANCIAL HIGHLIGHTS

Class E	Year Ended May 31, 2018		Year Ended May 31, 2017		Year Ended May 31, 2016		Year Ended May 29, 20151		Year Ended May 30, 20141
Per Share Operating Data
Net asset value, beginning of period		$1.00		$1.00		$1.00		$1.00		$1.00
Income (loss) from investment operations:
Net investment income2		0.01		0.003		0.003		0.003		0.003
Net realized gain (loss)		(0.00)3		0.003		0.003		0.003		0.003
Total from investment operations		0.01		0.003		0.003		0.003		0.003
Dividends and/or distributions to shareholders:
Dividends from net investment income		(0.01)		(0.00) 3		(0.00)3		(0.00)3		(0.00)3
Net asset value, end of period		$1.00		$1.00		$1.00		$1.00		$1.00
Total Return4		1.18%		0.46%		0.29%		0.10%		0.09%
Ratios/Supplemental Data
Net assets, end of period (in thousands)		$7,127,369		$6,039,613		$6,643,592		$5,783,350		$5,907,674
Average net assets (in thousands)		$6,339,648		$6,279,494		$6,484,183		$6,003,856		$6,291,038
Ratios to average net assets:5
Net investment income		1.19%		0.46%		0.29%		0.10%		0.09%
Total expenses		0.10%		0.11%		0.10%		0.10%		0.10%
Expenses after payments, waivers and/or reimbursements and reduction to custodian expenses		0.10%		0.11%		0.10%		0.10%		0.10%

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. Less than $0.005 per share.

4. 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 calculated on the last business day of the fiscal period. 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.

5. Annualized for periods less than one full year.

See accompanying Notes to Financial Statements.

18      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

Class L	Year Ended May 31, 2018		Year Ended May 31, 2017		Year Ended May 31, 2016		Year Ended May 29, 20151		Year Ended May 30, 20141
Per Share Operating Data
Net asset value, beginning of period		$1.00		$1.00		$1.00		$1.00		$1.00
Income (loss) from investment operations:
Net investment income2		0.01		0.003		0.003		0.003		0.003
Net realized gain (loss)		(0.00)3		0.003		0.003		0.003		0.003
Total from investment operations		0.01		0.003		0.003		0.003		0.003
Dividends and/or distributions to shareholders:
Dividends from net investment income		(0.01)		(0.00)3		(0.00)3		(0.00)3		(0.00)3
Net asset value, end of period		$1.00		$1.00		$1.00		$1.00		$1.00
Total Return4		1.12%		0.41%		0.24%		0.05%		0.04%
Ratios/Supplemental Data
Net assets, end of period (in thousands)		$221,575		$895,676		$798,272		$771,880		$873,074
Average net assets (in thousands)		$352,301		$846,273		$788,320		$830,945		$874,757
Ratios to average net assets:5
Net investment income		1.14%		0.41%		0.24%		0.05%		0.04%
Total expenses		0.16%		0.16%		0.16%		0.16%		0.16%
Expenses after payments, waivers and/or reimbursements and reduction to custodian expenses		0.16%		0.16%		0.16%		0.16%		0.16%

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. Less than $0.005 per share.

4. 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 calculated on the last business day of the fiscal period. 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.

5. Annualized for periods less than one full year.

See accompanying Notes to Financial Statements.

19      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

FINANCIAL HIGHLIGHTS Continued

Class P	Year Ended May 31, 2018		Year Ended May 31, 2017		Year Ended May 31, 2016		Year Ended May 29, 20151		Year Ended May 30, 20141
Per Share Operating Data
Net asset value, beginning of period		$1.00		$1.00		$1.00		$1.00		$1.00
Income (loss) from investment operations:
Net investment income2		0.01		0.003		0.003		0.003		0.003
Net realized gain (loss)		(0.00)3		0.003		0.003		0.003		0.003
Total from investment operations		0.01		0.003		0.003		0.003		0.003
Dividends and/or distributions to shareholders:
Dividends from net investment income		(0.01)		(0.00)3		(0.00)3		(0.00)3		(0.00)3
Net asset value, end of period		$1.00		$1.00		$1.00		$1.00		$1.00
Total Return4		1.12%		0.41%		0.24%		0.02%		0.01%
Ratios/Supplemental Data
Net assets, end of period (in thousands)		$8,171		$8,081		$8,047		$7,748		$13,797
Average net assets (in thousands)		$8,116		$8,060		$8,024		$10,514		$14,595
Ratios to average net assets:5
Net investment income		1.12%		0.41%		0.24%		0.01%		0.01%
Total expenses		0.40%		0.41%		0.40%		0.40%		0.40%
Expenses after payments, waivers and/or reimbursements and reduction to custodian expenses		0.17%		0.16%		0.15%		0.19%		0.18%

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. Less than $0.005 per share.

4. 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 calculated on the last business day of the fiscal period. 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.

5. Annualized for periods less than one full year.

See accompanying Notes to Financial Statements.

20      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

NOTES TO FINANCIAL STATEMENTS May 31, 2018

1. Organization

Oppenheimer Institutional Government Money Market Fund (the “Fund”) is registered under the Investment Company Act of 1940 (“1940 Act”), as amended, as a diversified open-end management investment company. The Fund’s investment objective is to seek income consistent with stability of principal. 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 E, Class L and Class P shares. Class E and Class L shares are sold at net asset value per share without any initial sales charge. Class E shares are only offered to other Oppenheimer Funds, the Manager and their affiliates. Class P shares will normally be sold at net asset value per share without any initial sales charge and are subject to a service plan. Class L and Class P shares are offered directly to institutional investors and may only be sold through an investment professional. Brokers or other investment professionals that offer Class L and Class P shares may impose charges on those accounts. 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.

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.

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 distributions, if any, are declared daily and paid monthly. Capital gain distributions, if any, are declared and paid annually but may be paid at other times to maintain the net asset value per share at $1.00.

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

21      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

NOTES TO FINANCIAL STATEMENTSContinued

2. Significant Accounting Policies (Continued)

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.

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 overdraft at a rate equal to the Prime Rate plus 0.35%. 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 May 31, 2018, including open tax years, and does not believe there are any uncertain tax positions requiring recognition in the Fund’s financial statements.

The tax components of capital shown in the following table represent distribution requirements the Fund must satisfy under the income tax regulations, losses the Fund may be able to offset against income and gains realized in future years for federal income tax purposes.

Undistributed Net Investment Income	Undistributed Long-Term Gain		Accumulated Loss Carryforward1,2,3
$192,155		$—		$41,139

1. At period end, the Fund had $41,139 of net capital loss carryforward available to offset future realized capital

22      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

2. Significant Accounting Policies (Continued)

gains, if any, and thereby reduce future taxable gain distributions. Details of the capital loss carryforwards are included in the table below. Capital loss carryovers with no expiration, if any, must be utilized prior to those with expiration dates.

Expiring
No expiration	$	41,139

2. During the reporting period, the Fund did not utilize any capital loss carryforwards.

3. During the previous reporting period, the Fund did not utilize any capital loss carryforwards.

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.

Accordingly, the following amounts have been reclassified for the reporting period. Net assets of the Fund were unaffected by the reclassifications.

	Reduction		Reduction
	to Accumulated		to Accumulated Net
Increase	Net Investment		Realized Gain
to Paid-in Capital	Loss		on Investments
$5,079		$67,750		$72,829

The tax character of distributions paid during the reporting periods:

	Year Ended		Year Ended
	May 31, 2018		May 31, 2017
Distributions paid from:
Ordinary income	$	79,423,190	$	32,111,245

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

23      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

NOTES TO FINANCIAL STATEMENTSContinued

3. Securities Valuation (Continued)

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 at cost adjusted by the amortization of discount or premium to maturity (amortized cost), which approximates market value. If amortized cost is determined not to approximate market value, the fair value of the portfolio securities will be determined under procedures approved by the Fund’s Board of Trustees.

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 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).

24      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

3. Securities Valuation (Continued)

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 measured using net asset value and 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 2—		Level 3—
	Level 1—		Other Significant		Significant
	Unadjusted		Observable		Unobservable
	Quoted Prices		Inputs		Inputs		Value
Assets Table
Investments, at Value:
U.S. Government Agencies	$	—	$	4,129,674,720	$	—	$	4,129,674,720
U.S. Government Obligations		—		54,586,745		—		54,586,745
Repurchase Agreements		—		3,162,000,000		—		3,162,000,000
Investment Companies		30,061,899		—		—		30,061,899
Total Assets	$	30,061,899	$	7,346,261,465	$	—	$	7,376,323,364

For the reporting period, there were no transfers between levels.

4. Investments and Risk

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 also invest in money market instruments directly or in other affiliated or unaffiliated money market funds.

Securities on a When-Issued or Delayed Delivery Basis. The Fund may purchase securities on a “when-issued” basis, and may purchase or sell securities on a “delayed delivery” basis. “When-issued” or “delayed delivery” refers to securities whose terms and indenture are available and for which a market exists, but which are not available for immediate delivery. Delivery and payment for securities that have been purchased by the Fund on a when-issued basis normally takes place within six months and possibly as long as two years or more after the trade date. During this period, such securities do not earn interest, are subject to market fluctuation and may increase or decrease in value prior to their delivery. The purchase of securities on a when-issued basis may increase the volatility of the Fund’s net asset value to the extent the Fund executes such transactions while remaining substantially fully invested. When the Fund engages in when-issued or delayed delivery transactions, it relies on the buyer or seller, as the case may be, to complete the transaction. Their failure to do so may cause the Fund to lose the opportunity to obtain or dispose of the security at a price and yield it considers advantageous. The Fund may also sell securities that it purchased on a when-issued basis or forward commitment prior to settlement of the original purchase.

25      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

NOTES TO FINANCIAL STATEMENTSContinued

4. Investments and Risk (Continued)

At period end, the Fund had sold securities issued on a delayed delivery basis as follows:

	When-Issued or Delayed Delivery Basis Transactions
Sold securities		$13,638,569

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:

26      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

6. Shares of Beneficial Interest (Continued)

	Year Ended May 31, 2018						Year Ended May 31, 2017
	Shares			Amount			Shares			Amount
Class E
Sold		51,551,361,784		$	51,551,361,784			49,050,475,878		$	49,050,475,878
Dividends and/or distributions reinvested		4,185,868			4,185,868			2,108,153			2,108,153
Redeemed		(50,467,778,587	)		(50,467,778,587	)		(49,656,629,160	)		(49,656,629,160	)
Net increase (decrease)		1,087,769,065		$	1,087,769,065			(604,045,129	)	$	(604,045,129)
Class L
Sold		1,914,790,118		$	1,914,790,118			7,905,578,093		$	7,905,578,093
Dividends and/or distributions reinvested		3,009,294			3,009,294			3,405,460			3,405,460
Redeemed		(2,591,906,864	)		(2,591,906,864	)		(7,811,586,616	)		(7,811,586,616	)
Net increase (decrease)		(674,107,452	)	$	(674,107,452	)		97,396,937		$	97,396,937
Class P
Sold		—		$	—			—		$	—
Dividends and/or distributions reinvested		90,000			90,000			33,170			33,170
Redeemed		—			—			—			—
Net increase		90,000		$	90,000			33,170		$	33,170

7. Fees and Other Transactions with Affiliates

Management Fees. Under the investment advisory agreement, the Fund pays the Manager a management fee based on the daily net assets of the Fund at an annual rate of 0.10%.

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

27      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

NOTES TO FINANCIAL STATEMENTSContinued

7. Fees and Other Transactions with Affiliates (Continued)

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 has adopted an unfunded retirement plan (the “Plan”) for the Fund’s Independent Trustees. Benefits are based on years of service and fees paid to each Trustee during their period of service. The Plan was frozen with respect to adding new participants effective December 31, 2006 (the “Freeze Date”) and existing Plan Participants as of the Freeze Date will continue to receive accrued benefits under the Plan. Active Independent Trustees as of the Freeze Date have each elected a distribution method with respect to their benefits under the Plan.

During the reporting period, the Fund’s projected benefit obligations, payments to retired Trustees and accumulated liability were as follows:

Projected Benefit Obligations Increased	$	—
Payments Made to Retired Trustees		22,623
Accumulated Liability as of May 31, 2018		195,088

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 Trustee 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 Trustee. The Fund purchases shares of the funds selected for deferral by the Trustee 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 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 P Shares. The Fund has adopted a Service Plan (the “Plan”) for Class P 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 P shares. Reimbursement is made periodically at an annual rate of up to 0.25% of the average annual net assets of Class P 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 P shares. Any unreimbursed expenses the Distributor incurs with respect to

28      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

7. Fees and Other Transactions with Affiliates (Continued)

Class P 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.

Waivers and Reimbursements of Expenses. The Manager has voluntarily agreed to waive fees and/or reimburse the Fund for certain expenses in order to limit “Expenses after waivers, payments and/or reimbursements and reduction to custodian fees” (excluding any applicable dividend expense, taxes, interest and fees from borrowing, any subsidiary expenses, brokerage commissions, unusual and infrequent expenses, and certain other Fund expenses not incurred in the ordinary course of the Fund’s business) to an annual rate of 0.24% for Class P shares calculated on the daily net assets of the Fund.

The Manager has also voluntarily undertaken to waive management fees and/or reimburse expenses (but not below zero) to the extent necessary to assist the Fund in attempting to maintain a positive yield. There is no guarantee that the Fund will maintain a positive yield.

The Distributor has contractually undertaken to waive the fees payable under the Service Plan for Class P shares so that those fees are limited to 0.05% of the average annual net assets for Class P shares of the Fund. During the reporting period, the Distributor waived $19,140 for Class P shares.

The Manager is permitted to recapture previously waived and/or reimbursed fees in any given fiscal year if the recapture would not: 1) cause the Fund to generate a negative daily yield, and 2) exceed amounts previously waived and/or reimbursed under this arrangement during the current and prior three fiscal years. The reimbursement to the Manager of such previous waivers and reimbursements would not include any portion of distribution and/or service fees. At period end, there are no amounts eligible for recapture. The Manager has not recaptured any previously waived and/or reimbursed amounts during the reporting period.

Waivers and/or reimbursements may be modified or terminated as set forth according to the terms in the prospectus.

8. Repurchase Agreements

In a repurchase transaction, a Fund buys a security and simultaneously sells it back to an approved institution for delivery on an agreed-upon future date. The resale price exceeds the purchase price by an amount that reflects an agreed-upon interest rate effective for the period during which the repurchase agreement is in effect. Approved institutions include U.S. commercial banks, U.S. branches of foreign banks or broker-dealers that have been designated as primary dealers in government securities. They must meet credit requirements set by the investment adviser from time to time. Repurchase agreements must be fully collateralized. However, if the seller fails to pay the repurchase price on the delivery date, a Fund may incur costs in disposing of the collateral and may experience losses if there is any delay in its ability to do so. If the default on the part of the seller is due to its bankruptcy, a Fund’s ability to liquidate the collateral may be delayed or limited.

The following is a summary by counterparty of the market value of Borrowings and Other

29      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

NOTES TO FINANCIAL STATEMENTSContinued

8. Repurchase Agreements (Continued)

Financing Transactions and collateral (received) as of period end:

Counterparty	Repurchase Agreement Proceeds to be Received1		Collateral Received1		Net Exposure2
Repurchase Agreements
Credit Agricole Corp. & Investment Bank		$104,150,800		$(106,233,816)		$(2,083,016)
Credit Agricole Corp. & Investment Bank		65,097,392		(66,399,340)		(1,301,948)
Credit Agricole Corp. & Investment Bank		175,008,507		(178,508,677)		(3,500,170)
Credit Agricole Corp. & Investment Bank		303,514,838		(309,585,135)		(6,070,297)
Deusche Bank Securities, Inc.		75,058,001		(82,563,801)		(7,505,800)
Deusche Bank Securities, Inc.		169,408,423		(186,349,266)		(16,940,843)
INTL FCStone Financial, Inc.		135,020,956		(139,102,513)		(4,081,557)
INTL FCStone Financial, Inc.		60,013,009		(62,597,413)		(2,584,404)
RBC Dominion Securities, Inc.		421,820,536		(430,256,947)		(8,436,411)
Royal Bank of Canada		376,318,397		(383,844,765)		(7,526,368)
South Street Securities LLC		500,073,750		(510,075,225)		(10,001,475)
South Street Securities LLC		498,024,900		(507,985,398)		(9,960,498)
TD Securities (USA) LLC		145,007,090		(147,907,232)		(2,900,142)
TD Securities (USA) LLC		134,007,031		(136,687,171)		(2,680,140)
		$3,162,523,630

1. Includes accrued interest.

2. Net exposure represents the net receivable/payable that would be due from the counterparty in the event of default.

30      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the Shareholders and Board of Trustees

Oppenheimer Institutional Government Money Market Fund:

Opinion on the Financial Statements

We have audited the accompanying statement of assets and liabilities of Oppenheimer Institutional Government Money Market Fund (the “Fund”), including the statement of investments, as of May 31, 2018, the related statement of operations for the year then ended, the statements of changes in net assets for each of the years in the two year period then ended, and the related notes (collectively, the “financial statements”) and the financial highlights for each of the years in the five year period then ended. In our opinion, the financial statements and financial highlights present fairly, in all material respects, the financial position of the Fund as of May 31, 2018, the results of its operations for the year then ended, the changes in its net assets for each of the years in the two year period then ended, and the financial highlights for each of the years in the five year period then ended, in conformity with U.S. generally accepted accounting principles.

Basis for Opinion

These financial statements and financial highlights are the responsibility of the Fund’s management. Our responsibility is to express an opinion on these financial statements and financial highlights based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (“PCAOB”) and are required to be independent with respect to the Fund in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements and financial highlights are free of material misstatement, whether due to error or fraud. Our audits included performing procedures to assess the risks of material misstatement of the financial statements and financial highlights, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements and financial highlights. Such procedures also included confirmation of securities owned as of May 31, 2018, by correspondence with the custodian and brokers, or by other appropriate auditing procedures. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements and financial highlights. We believe that our audits provide a reasonable basis for our opinion.

KPMG LLP

We have not been able to determine the specific year that we began serving as the auditor of one or more Oppenheimer Funds investment companies, however we are aware that we have served as the auditor of one or more Oppenheimer Funds investment companies since at least 1969.

Denver, Colorado

July 25, 2018

31      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

FEDERAL INCOME TAX INFORMATION Unaudited

In early 2018, if applicable, shareholders of record received information regarding all dividends and distributions paid to them by the Fund during calendar year 2017.

None of the dividends paid by the Fund during the reporting period are eligible for the corporate dividend-received deduction.

Dividends, if any, paid by the Fund during the reporting period which are not designated as capital gain distributions, may be eligible for lower individual income tax rates to the extent that the Fund has received qualified dividend income as stipulated by recent tax legislation. In early 2018, shareholders of record received information regarding the percentage of distributions that are eligible for lower individual income tax rates. The amount will be the maximum amount allowed.

Recent tax legislation allows a regulated investment company to designate distributions not designated as capital gain distributions, as either interest related dividends or short-term capital gain dividends, both of which are exempt from the U.S. withholding tax applicable to non U.S. taxpayers. For the reporting period, the maximum amount allowable but not less than $79,444,245 of the ordinary distributions to be paid by the Fund qualifies as an interest related dividend.

The foregoing information is presented to assist shareholders in reporting distributions received from the Fund to the Internal Revenue Service. Because of the complexity of the federal regulations which may affect your individual tax return and the many variations in state and local tax regulations, we recommend that you consult your tax advisor for specific guidance.

32      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

PORTFOLIO PROXY VOTING POLICIES AND GUIDELINES;

UPDATES TO STATEMENT OF INVESTMENT 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.

33      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET 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 the 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. If the Fund (or an underlying fund in which the Fund invests) invests in real estate investment trusts (REITs) and/or master limited partnerships (MLPs), the percentages attributed to each category are estimated using historical information because the character of the amounts received from the REITs and/or MLPs in which the Fund (or underlying 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 Institutional Government Money Market Fund		3/29/18		99.8%		0.0%		0.2%
Oppenheimer Institutional Government Money Market Fund		5/31/18		99.7%		0.0%		0.3%

34      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

TRUSTEES AND OFFICERS Unaudited

Name, Position(s) Held with the Fund, Length of Service, Year of Birth	Principal Occupation(s) During the Past 5 Years; Other Trusteeships/ Directorships Held; Number of Portfolios in the Fund Complex Currently Overseen
INDEPENDENT TRUSTEES	The address of each Trustee in the chart below is 6803 S. Tucson Way, Centennial, Colorado 80112-3924. Each Trustee serves for an indefinite term, or until his or her resignation, retirement, death or removal.
Brian F. Wruble, Chairman of the Board of Trustees (since 2007) and Trustee (since 2006) Year of Birth: 1943	Governor of Community Foundation of the Florida Keys (non-profit) (since July 2012); Director of TCP Capital, Inc. (registered business development company) (since November 2015); Chairman Emeritus of the Board of Trustees (since August 2011), Chairman of the Board of Trustees (August 2007-August 2011), Trustee of the Board of Trustees (since August 1991) of The Jackson Laboratory (non-profit); Member of Zurich Insurance Group’s Investment Management Advisory Council (insurance) (October 2004-February 2017); Treasurer (since 2007) and Trustee (since May 1992) of the Institute for Advanced Study (non-profit educational institute); Director of Special Value Opportunities Fund, LLC (registered investment company) (affiliate of the Sub-Adviser’s parent company) (September 2004- June 2015); General Partner of Odyssey Partners, L.P. (hedge fund) (September 1995-December 2007); Special Limited Partner of Odyssey Investment Partners, LLC (private equity investment) (January 1999-September 2004). Oversees 51 portfolios in the OppenheimerFunds complex. Mr. Wruble has served on the Boards of certain Oppenheimer funds since April 2001, during which time he has become familiar with the Fund’s (and other Oppenheimer funds’) financial, accounting, regulatory and investment matters and has contributed to the Board’s deliberations.
Beth Ann Brown, Trustee (since 2016) Year of Birth: 1968	Director, Board of Directors of Caron Engineering Inc. (since January 2018); Advisor, Board of Advisors of Caron Engineering Inc. (December 2014-December 2017); Independent Consultant (since September 2012); held the following positions at Columbia Management Investment Advisers LLC: Head of Intermediary Distribution (2008-2012), Managing Director, Strategic Relations (2005-2008), Managing Director, Head of National Accounts (2004-2005); Senior Vice President, National Account Manager (2002-2004), Senior Vice President, Key Account Manager (1999-2002) and Vice President, Key Account Manager (1996-1999) of Liberty Funds Distributor, Inc.; President and Director, of Acton Shapleigh Youth Conservation Corps (non -profit) (2012-2015); and Vice President and Director of Grahamtastic Connection (non-profit) (since May 2013). Oversees 51 portfolios in the OppenheimerFunds complex. Ms. Brown has served on the Boards of certain Oppenheimer funds since January 2016, during which time she has become familiar with the Fund’s (and other Oppenheimer funds’) financial, accounting, regulatory and investment matters and has contributed to the Board’s deliberations.
Edmund P. Giambastiani, Jr., Trustee (since 2013) Year of Birth: 1948	Director of THL Credit, Inc. (since November 2016) (alternative credit investment manager); Advisory Board Member of the Maxwell School of Citizenship and Public Affairs of Syracuse University (April 2012-September 2016); Director of Mercury Defense Systems Inc. (information technology) (August 2011-February 2013); Trustee of the U.S. Naval Academy Foundation Athletic & Scholarship Program (since November 2010); Advisory Board Member of the Massachusetts Institute of Technology Lincoln Laboratory (federally-funded research development) (since May

35      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

TRUSTEES AND OFFICERS Unaudited/ Continued

Edmund P. Giambastiani, Jr., Continued

2010); Director of The Boeing Company (aerospace and defense) (since October 2009); Trustee of MITRE Corporation (federally-funded research development) (since September 2008); Independent Director of QinetiQ Group Plc (defense technology and security) (February 2008-August 2011); Chairman of Monster Worldwide, Inc. (career services) (March 2015-November 2016), Director of Monster Worldwide, Inc. (career services) (February 2008-June 2011); Lead Director (June 2011-March 2015); Chairman of Alenia North America, Inc. (military and defense products) (January 2008-October 2009); Director of SRA International, Inc. (information technology and services) (January 2008-July 2011); President of Giambastiani Group LLC (national security and energy consulting) (since October 2007); United States Navy, career nuclear submarine officer (June 1970-October 2007); Seventh Vice Chairman of the Joint Chiefs of Staff (2005-October 2007); Supreme Allied Commander of NATO Allied Command Transformation (2003-2005) and Commander, U.S. Joint Forces Command (2002-2005). Since his retirement from the U.S. Navy in October 2007, Admiral Giambastiani has also served on numerous U.S. Government advisory boards, investigations and task forces for the Secretaries of Defense, State and Interior and the Central Intelligence Agency. He recently completed serving as a federal commissioner on the Military Compensation and Retirement Modernization Commission. Oversees 51 portfolios in the OppenheimerFunds complex. Admiral Giambastiani has served on the Boards of certain Oppenheimer funds since February 2013, including as an Advisory Board Member for certain Oppenheimer funds, during which time he has become familiar with the Fund’s (and other Oppenheimer funds’) financial, accounting, regulatory and investment matters and has contributed to the Board’s deliberations. For purposes of this report, Admiral Giambastiani is identified as a Trustee.

Elizabeth Krentzman, Trustee (since 2014) Year of Birth: 1959

Trustee of the University of Florida National Board Foundation (since September 2017); Member of the Cartica Funds Board of Directors (private investment funds) (since January 2017); Member of the University of Florida Law Center Association, Inc. Board of Trustees and Audit Committee Member (since April 2016); Member of University of Florida Law Advisory Board, Washington, DC Alumni Group (since 2015); Advisory Board Member of the Securities and Exchange Commission Historical Society (since 2007); held the following positions at Deloitte & Touche LLP: Principal and Chief Regulatory Advisor for Asset Management Services (2007 - 2014) and U.S. Mutual Fund Leader (2011 - 2014); General Counsel of the Investment Company Institute (trade association) (June 2004 - April 2007); held the following positions at Deloitte & Touche LLP: National Director of the Investment Management Regulatory Consulting Practice (1997 - 2004), Principal (2003 - 2004), Director (1998 - 2003) and Senior Manager (1997 - 1998); Assistant Director of the Division of Investment Management – Office of Disclosure and Investment Adviser Regulation of the U.S. Securities and Exchange Commission (1996 - 1997) and various positions with the Division of Investment Management – Office of Regulatory Policy (1991 - 1996) of the U.S. Securities and Exchange Commission; Associate at Ropes & Gray LLP (1987 – 1991). Oversees 51 portfolios in the OppenheimerFunds complex. Ms. Krentzman has served on the Boards of certain Oppenheimer funds since August 2014, during which time she has become familiar with the Fund’s (and other Oppenheimer funds’) financial, accounting, regulatory and investment matters and has contributed to the Board’s deliberations.

36      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

Mary F. Miller, Trustee (since 2006) Year of Birth: 1942	Trustee of International House (not-for-profit) (since June 2007); Trustee of the American Symphony Orchestra (not-for-profit) (October 1998-November 2011); and Senior Vice President and General Auditor of American Express Company (financial services company) (July 1998-February 2003). Oversees 51 portfolios in the OppenheimerFunds complex. Ms. Miller has served on the Boards of certain Oppenheimer funds since August 2004, during which time she has become familiar with the Fund’s (and other Oppenheimer funds’) financial, accounting, regulatory and investment matters and has contributed to the Board’s deliberations.
Joel W. Motley, Trustee (since 2006) Year of Birth: 1952	Director of Office of Finance Federal Home Loan Bank (since September 2016); Director of Greenwall Foundation (since October 2013); Member of Board and Investment Committee of The Greenwall Foundation (since April 2013); Member of the Vestry of Trinity Wall Street (since April 2012); Director of Southern Africa Legal Services Foundation (since March 2012); Board Member and Investment Committee Member of Pulitzer Center for Crisis Reporting (non-profit journalism) (since March 2011); Managing Director of Public Capital Advisors, LLC (privately- held financial advisor) (since January 2006); Managing Director of Carmona Motley, Inc. (privately-held financial advisor) (since January 2002); Director of Columbia Equity Financial Corp. (privately-held financial advisor) (2002-2007); Managing Director of Carmona Motley Hoffman Inc. (privately-held financial advisor) (January 1998-December 2001); Member of the Finance and Budget Committee of the Council on Foreign Relations, Member of the Investment Committee and Board of Human Rights Watch (since July 2000) and Member of the Investment Committee and Board of Historic Hudson Valley (since February 2010). Oversees 51 portfolios in the OppenheimerFunds complex. Mr. Motley has served on the Boards of certain Oppenheimer funds since October 2002, during which time he has become familiar with the Fund’s (and other Oppenheimer funds’) financial, accounting, regulatory and investment matters and has contributed to the Board’s deliberations.
Joanne Pace, Trustee (since 2013) Year of Birth: 1958	Advisory Board Director of Massey Quick Simon & Co. (wealth management), LLC (since October 2014); Board Director of Horizon Blue Cross Blue Shield of New Jersey (healthcare) (since November 2012); Advisory Board Director of The Alberleen Group LLC (investment banking) (since March 2012); Governing Council Member (since 2016) and Chair of Education Committee (since 2017) of Independent Directors Council (IDC) (since 2016); Board Member of 100 Women in Finance (non-profit) (since January 2015); Advisory Council Member of Morgan Stanley Children’s Hospital (non-profit) (since May 2012); Director of The Komera Project (non-profit) (April 2012-2016); New York Advisory Board Director of Peace First (non-profit) (March 2010-2013); Senior Advisor of SECOR Asset Management, LP (2010-2011); Managing Director and Chief Operating Officer of Morgan Stanley Investment Management (2006-2010); Partner and Chief Operating Officer of FrontPoint Partners, LLC (hedge fund) (2005-2006); held the following positions at Credit Suisse (investment banking): Managing Director (2003-2005); Global Head of Human Resources and member of Executive Board and Operating Committee (2004-2005), Global Head of Operations and Product Control (2003-2004); held the following positions at Morgan Stanley: Managing Director (1997-2003), Controller and Principal Accounting Officer (1999-2003); Chief Financial Officer (temporary assignment) for the Oversight Committee, Long Term Capital Management (1998-1999). Lead Independent Director and Chair of the Audit and Nominating Committee of The Global Chartist Fund, LLC of Oppenheimer Asset Management (2011-2012); Board Director of Managed Funds Association (2008-2010); Board Director of Morgan Stanley Foundation (2007- 2010) and Investment Committee Chair (2008-2010). Oversees 51 portfolios in the

37      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

TRUSTEES AND OFFICERS Unaudited / Continued

Joanne Pace, Continued	OppenheimerFunds complex. Ms. Pace has served on the Boards of certain Oppenheimer funds since November 2012, including as an Advisory Board Member for certain Oppenheimer funds, during which time she has become familiar with the Fund’s (and other Oppenheimer funds’) financial, accounting, regulatory and investment matters and has contributed to the Board’s deliberations. For purposes of this report, Ms. Pace is identified as a Trustee.
Daniel Vandivort, Trustee (since 2014) Year of Birth: 1954	Chairman and Lead Independent Director/Trustee (March 2010-September 2014), Chairman of the Audit Committee (March 2009-September 2014) and Director/ Trustee (December 2008-September 2014) of the Board of Directors/Trustees of Value Line Funds; Trustee (since January 2015) and Treasurer and Chairman of the Audit Committee and Finance Committee (since January 2016) of Board of Trustees of Huntington Disease Foundation of America; Trustee, Board of Trustees, RIM Retirement Savings Plan (2005-2007); President and Chief Investment Officer, Robeco Investment Management, formerly known as Weiss Peck and Greer (January 2005-June 2007); Member, Management Committee of Robeco Investment Management (2001-2007); Chairman and Trustee of the Board of Trustees of Weiss, Peck and Greer Funds (2004-2005); Managing Director and Head of Fixed Income, Weiss, Peck and Greer (November 1994-January 2005); Managing Director and Head of Fixed Income, CS First Boston Investment Management (January 1992-November 1994); Director, Global Product Development, First Boston Asset Management (November 1989-January 1992); Vice President, Fixed Income Sales, First Boston Corp. (May 1984-November 1989). Oversees 51 portfolios in the OppenheimerFunds complex. Mr. Vandivort has served on the Boards of certain Oppenheimer funds since 2014, during which time he has become familiar with the Fund’s (and other Oppenheimer funds’) financial, accounting, regulatory and investment matters and has contributed to the Board’s deliberations.
INTERESTED TRUSTEE AND OFFICER	Mr. Steinmetz is an “Interested Trustee” because he is affiliated with the Manager and the Sub-Adviser by virtue of his positions as Chairman of the Sub-Adviser and officer and director of the Manager. Both as a Trustee and as an officer, Mr. Steinmetz serves for an indefinite term, or until his resignation, retirement, death or removal. Mr. Steinmetz’s address is 225 Liberty Street, New York, New York 10281-1008.
Arthur P. Steinmetz, Trustee (since 2015), President and Principal Executive Officer (since 2014) Year of Birth: 1958	Chairman of OppenheimerFunds, Inc. (since January 2015); CEO and Chairman of OFI Global Asset Management, Inc. (since July 2014), President of OFI Global Asset Management, Inc. (since May 2013), a Director of OFI Global Asset Management, Inc. (since January 2013), Director of OppenheimerFunds, Inc. (since July 2014), President, Management Director and CEO of Oppenheimer Acquisition Corp. (OppenheimerFunds, Inc.’s parent holding company) (since July 2014), and President and Director of OFI SteelPath, Inc. (since January 2013). Chief Investment Officer of the OppenheimerFunds advisory entities from (January 2013-December 2013); Executive Vice President of OFI Global Asset Management, Inc. (January 2013-May 2013); Chief Investment Officer of OppenheimerFunds, Inc. (October 2010-December 2012); Chief Investment Officer, Fixed-Income, of OppenheimerFunds, Inc. (April 2009-October 2010); Executive Vice President of OppenheimerFunds, Inc. (October 2009-December 2012); Director of Fixed Income of OppenheimerFunds, Inc. (January 2009-April 2009); and a Senior Vice President of OppenheimerFunds, Inc. (March 1993-September 2009). An officer of 107 portfolios in the OppenheimerFunds complex.

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OTHER OFFICERS OF THE FUND	The addresses of the Officers in the chart below are as follows: for Mss. Lo Bessette, Foxson and Picciotto, 225 Liberty Street, New York, New York 10281-1008, for Messrs. Proctor, Wilde and Petersen, 6803 S. Tucson Way, Centennial, Colorado 80112-3924. Each Officer serves for an indefinite term or until his or her resignation, retirement, death or removal.
Christopher Proctor, Vice President (since 2010) Year of Birth: 1968	Head of the Cash Strategies Team (since July 2013); Senior Vice President of the Sub-Adviser (since July 2013); Senior Portfolio Manager of the Sub-Adviser (since January 2010); Vice President of the Sub-Adviser (August 2008-July 2013). Vice President at Calamos Asset Management (January 2007-March 2008); Scudder- Kemper Investments (1999-2002); Managing Director and Co-Founder of Elmhurst Capital Management (June 2004-January 2007); Senior Manager of Research for Etrade Global Asset Management (2002-2004). A portfolio manager and officer of other portfolios in the OppenheimerFunds complex.
Adam S. Wilde, Vice President (since 2013) Year of Birth: 1978	Vice President of the Sub-Adviser (since May 2011) and a Portfolio Manager of the Sub-Adviser (since July 2013). He served as the head of credit research for the cash strategies team of the Sub-Adviser (from 2011 to 2013), and as an Assistant Vice President and Senior Research Analyst of the Sub-Adviser (from 2008 to 2011). Mr. Wilde served as an Intermediate Research Analyst of the Sub-Adviser (from 2007 to 2008) and served in other analyst roles of the Sub-Adviser (since 2002). Mr. Wilde joined the Sub-Adviser in 2001. A portfolio manager and officer of other portfolios in the OppenheimerFunds complex.
Cynthia Lo Bessette, Secretary and Chief Legal Officer (since 2016) Year of Birth: 1969	Executive Vice President, General Counsel and Secretary of OFI Global Asset Management, Inc. (since February 2016); Senior Vice President and Deputy General Counsel of OFI Global Asset Management, Inc. (March 2015-February 2016); Chief Legal Officer of OppenheimerFunds, Inc. and OppenheimerFunds Distributor, Inc. (since February 2016); Vice President, General Counsel and Secretary of Oppenheimer Acquisition Corp. (since February 2016); General Counsel of OFI SteelPath, Inc., OFI Advisors, LLC and Index Management Solutions, LLC (since February 2016); Chief Legal Officer of OFI Global Institutional, Inc., HarbourView Asset Management Corporation, OFI Global Trust Company, Oppenheimer Real Asset Management, Inc., OFI Private Investments Inc., Shareholder Services, Inc. and Trinity Investment Management Corporation (since February 2016); Corporate Counsel (February 2012-March 2015) and Deputy Chief Legal Officer (April 2013-March 2015) of Jennison Associates LLC; Assistant General Counsel (April 2008-September 2009) and Deputy General Counsel (October 2009-February 2012) of Lord Abbett & Co. LLC. An officer of 107 portfolios in the OppenheimerFunds complex.
Jennifer Foxson, Vice President and Chief Business Officer (since 2014) Year of Birth: 1969	Senior Vice President of OppenheimerFunds Distributor, Inc. (since June 2014); Vice President of OppenheimerFunds Distributor, Inc. (April 2006-June 2014); Vice President of OppenheimerFunds, Inc. (January 1998-March 2006); Assistant Vice President of OppenheimerFunds, Inc. (October 1991-December 1998). An officer of 107 portfolios in the OppenheimerFunds complex.

39      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

TRUSTEES AND OFFICERS Unaudited / Continued

Mary Ann Picciotto, Chief Compliance Officer and Chief Anti-Money Laundering Officer (since 2014) Year of Birth: 1973

Senior Vice President and Chief Compliance Officer of OFI Global Asset Management, Inc. (since March 2014); Chief Compliance Officer of OppenheimerFunds, Inc., OFI SteelPath, Inc., OFI Global Institutional, Inc., Oppenheimer Real Asset Management, Inc., OFI Private Investments Inc., Harborview Asset Management Corporation, Trinity Investment Management Corporation, and Shareholder Services, Inc. (since March 2014); Managing Director of Morgan Stanley Investment Management Inc. and certain of its various affiliated entities; Chief Compliance Officer of various Morgan Stanley Funds (May 2010-January 2014); Chief Compliance Officer of Morgan Stanley Investment Management Inc. (April 2007-January 2014). An officer of 107 portfolios in the OppenheimerFunds complex.

Brian S. Petersen, Treasurer and Principal Financial & Accounting Officer (since 2016) Year of Birth: 1970

Senior Vice President of OFI Global Asset Management, Inc. (since January 2017); Vice President of OFI Global Asset Management, Inc. (January 2013-January 2017); Vice President of OppenheimerFunds, Inc. (February 2007-December 2012); Assistant Vice President of OppenheimerFunds, Inc. (August 2002-2007). An officer of 89 portfolios in the OppenheimerFunds complex.

The Fund’s Statement of Additional Information contains additional information about the Fund’s Trustees and Officers is available without charge upon request, by calling 1.800.CALL OPP (225.5677).

40      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET FUND

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	Kramer Levin Naftalis & Frankel LLP

© 2018 OppenheimerFunds, Inc. All rights reserved.

41      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET 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.

42      OPPENHEIMER INSTITUTIONAL GOVERNMENT MONEY MARKET 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).

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	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. RA0647.001.0518 July 25, 2018

Item 2. Code of Ethics.

The registrant has adopted a code of ethics that applies to the registrant’s principal executive officer, principal financial officer, principal accounting officer or controller or persons performing similar functions.

Item 3. Audit Committee Financial Expert.

The Board of Trustees of the registrant has determined that Joanne Pace, the Board’s Audit Committee Chairwoman, is an audit committee financial expert and that Ms. Pace is “independent” for purposes of this Item 3.

Item 4. Principal Accountant Fees and Services.

(a) Audit Fees

The principal accountant for the audit of the registrant’s annual financial statements billed $30,800 in fiscal 2018 and $29,800 in fiscal 2017.

(b) Audit-Related Fees

The principal accountant for the audit of the registrant’s annual financial statements billed no such fees in fiscal 2018 and no such fees in fiscal 2017.

The principal accountant for the audit of the registrant’s annual financial statements billed $343,361 in fiscal 2018 and $320,775 in fiscal 2017 to the registrant’s investment adviser or any entity controlling, controlled by, or under common control with the adviser that provides ongoing services to the registrant.

Such services include: Internal control reviews, GIPS attestation procedures, custody audits, CP Conduit fees, incremental, and additional, audit services

(c) Tax Fees

The principal accountant for the audit of the registrant’s annual financial statements billed no such fees in fiscal 2018 and no such fees in fiscal 2017.

The principal accountant for the audit of the registrant’s annual financial statements billed $709,285 in fiscal 2018 and $710,577 in fiscal 2017 to the registrant’s investment adviser or any entity controlling, controlled by, or under common control with the adviser that provides ongoing services to the registrant.

Such services include: tax compliance, tax planning and tax advice. Tax compliance generally involves preparation of original and amended tax returns, claims for a refund and tax payment-planning services. Tax planning and tax advice includes assistance with tax audits and appeals, tax advice related to mergers and acquisitions and requests for rulings or technical advice from taxing authorities.

(d) All Other Fees

The principal accountant for the audit of the registrant’s annual financial statements billed no such fees in fiscal 2018 and no such fees in fiscal 2017.

The principal accountant for the audit of the registrant’s annual financial statements billed no such fees in fiscal 2018 and no such fees in fiscal 2017 to the registrant’s investment adviser or any entity controlling, controlled by, or under common control with the adviser that provides ongoing services to the registrant.

Such fees would include the cost to the principal accountant of attending audit committee meetings and consultations regarding the registrant’s retirement plan with respect to its Trustees.

(e) (1) During its regularly scheduled periodic meetings, the registrant’s audit committee will pre-approve all audit, audit-related, tax and other services to be provided by the principal accountants of the registrant.

The audit committee has delegated pre-approval authority to its Chairwoman for any subsequent new engagements that arise between regularly scheduled meeting dates provided that any fees such pre-approved are presented to the audit committee at its next regularly scheduled meeting.

Under applicable laws, pre-approval of non-audit services may be waived provided that: 1) the aggregate amount of all such services provided constitutes no more than five percent of the total amount of fees paid by the registrant to its principal accountant during the fiscal year in which services are provided 2) such services were not recognized by the registrant at the time of engagement as non-audit services and 3) such services are promptly brought to the attention of the audit committee of the registrant and approved prior to the completion of the audit.

(2) 0%

(f) Not applicable as less than 50%.

(g) The principal accountant for the audit of the registrant’s annual financial statements billed $1,052,646 in fiscal 2018 and $1,031,352 in fiscal 2017 to the registrant and the registrant’s investment adviser or any entity controlling, controlled by, or under common control with the adviser that provides ongoing services to the registrant related to non-audit fees. Those billings did not include any prohibited non-audit services as defined by the Securities Exchange Act of 1934.

(h) The registrant’s audit committee of the board of Trustees has considered whether the provision of non-audit services that were rendered to the registrant’s investment adviser, and any entity controlling, controlled by, or under common control with the investment adviser that provides ongoing services to the registrant that were not pre-approved pursuant to paragraph (c)(7)(ii) of Rule 2-01 of Regulation S-X is compatible with maintaining the principal accountant’s independence. No such services were rendered.

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 5/31/2018, 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 Institutional Government Money Market Fund

By:	/s/ Arthur P. Steinmetz
	Arthur P. Steinmetz
	Principal Executive Officer
Date:	7/20/2018

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:	7/20/2018

By:	/s/ Brian S. Petersen
	Brian S. Petersen
	Principal Financial Officer
Date:	7/20/2018