Exhibit (c)(19)

PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Project Francis Conflicts Committee GP LLC Discussion Materials of the Board of Directors of Arkose May 18, 2018 STRICTLY PRIVATE AND CONFIDENTIAL. This document is being sent to you for your information only as an investment banking clie nt of Goldman Sachs and should not be forwarded outside of your organization. This document has been prepared by the Investment Banking Division and is not a product of Goldman Sachs Global Investment Research. This document should not be used as a basis for trading in the securities or loans of the compani es named herein or for any other investment decision. This document does not constitute an offer to sell the securities or loans of the companies named herein or a solicitation of proxies or votes and should not be construed as consisting of investment advice. Goldman Sachs does not provide accounting, tax, or legal advice.

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PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Illustrative Summary Comparison of Potential Structural Alternatives (Preliminary analysis subject to final structure and further simplification) GP Buys Midstream GP Buys Midstream --“C-Corp NewCo” Summary Description  GP acquires Midstream in a 100% share transaction GP remains a partnership taxable as a corporation   GP acquires Midstream C-corp formed as Newco and becomes publicly traded surviving corporation  IDR Elimination? Yes Yes Midstream Equity Value  1 common pool of equity (1099) Mkt. Cap.  Same as GP Buys Midstream Float Midstream ---- GP $8.5bn $3.8bn Cash Distribution Potential  [To be further reviewed – typically a non-taxable merger with no basis step up, resulting in incremental tax leakage vs. Status Quo]  Increased vs. status quo: cash tax savings due to taxable transaction to target unitholders IDR LLC Series B Treatment  Requires renegotiation or conversion of Series B interest as part of transaction  Potential Change of Control for Series B units, which would result in vesting and exchange right Governance  Partnership-style (absent change to status quo)  Corporate-style Broad-based Equity Index Potential  No as result of i) LP status of remaining entities, and ii) partnership-style governance are both specifically excluded from broad-based indices  Yes – removes both “red flags” for broad-based index inclusion Unitholder / Shareholder Approvals  Midstream: Approval of majority of outstanding LP unitholders (53% held by Upstream) GP: Approval required if GP shares exchanged or converted and NewCo is trading entity  Midstream: Approval of majority of outstanding LP unitholders (53% held by Upstream) GP: Not required   2

PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Summary Observations on Potential Shareholder Reaction to an Arkose Simplification 1099 vs K-1 Securities Pro Forma Grow  Growth Rate: Pro forma entity, however, would still have a sector-leading growth rate and exceed Liquidity / Governance 3  Elevated Volumes: An event that leads to elevated trading volumes could cause some investors to reduce their positions given underlying weakness in the broader MLP market  Governance: A switch to more traditional governance, where voting rights are equal to economic participation, would strengthen sentiment from many key midstream investors who are increasingly vocal about lack of midstream governance  Investor Overlap: Substantial overlap in Midstream and GP’s investor bases at the institutional level; possible that some may invest in GP as a levered play on Midstream’s underlying assets — Lower “non-levered” growth rate may cause certain investors scale back their Arkose position th Midstream’s current growth profile — Change in growth profile, in isolation, is unlikely to result in meaningful selling  Depth of Market: The investor following and liquidity of the Midstream/Energy C-Corp market is significantly deeper than that of the MLP market — 505 investors are invested in the AMZ companies, with the top 20 managing a combined $2.2 trillion in AUM — Comparatively, 3,600+ investors have positions in Energy companies the S&P 1500, with the top 20 managing a combined $7.4 trillion in equity AUM  Dedicated Funds: While some funds are prevented from owning MLPs, we are not aware of any MLP-dedicated fund that is prevented from owning 1099 securities

PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Midstream Delaware Corporations vs. 1099 GPs Investment Observations Top 25 Midstream Delaware Corporation Active Investors Equity AUM ($mm) Delaware Corps Pos. ($mm)¹ 1099 GPs Pos. ($mm)² AMZ Pos. ($mm)  Meaningful overlap between top active Midstream 1099 GP Partnership investors and Midstream Delaware Corporation investors, suggesting indifference between 1099 structures Investor Tortoise Capital 15,502 1,525 213 10,455 Kayne Anderson 7,956 1,067 84 5,475 GSAM 139,583 1,045 104 5,325 Harvest 8,978 830 82 6,245 ClearBridge 111,692 660 48 3,315  Of the top 50 Midstream Delaware C-Corp investors, 12 do not hold any positions in 1099 GPs Neuberger Berman 91,995 639 2 1,658 Salient Capital 5,804 628 213 2,311 Deutsche AM 13,719 558 34 689 — But 7 of those investors hold positions in MLPs, suggesting governance is not the driving factor of their lack of investment Chickasaw Capital 4,804 552 230 2,455 OFI SteelPath 9,746 510 336 7,076 Fidelity 1,222,242 390 1 1,807 Eagle Global 3,230 378 102 1,353 FPR Partners 4,659 370 95 0 JP Morgan AM 349,427 349 41 0 Cushing 3,337 342 76 1,946 CIBC Atlantic Trust 23,316 340 42 2,593 UBS Financial Services, Inc. 180,549 328 4 3,745 BlackRock (UK) 320,409 291 1 0 Millennium 69,332 287 42 0 Source: Thomson Reuters as of 4Q 2017. Note: Blue shading denotes no overlap between Delaware C-Corp investors and 1099 GPs. ¹ Delaware Corp peers include KMI, OKE, SEMG, and TRGP. ² 1099 GP peers include AMGP, ENLC, and TEGP. 4 Total (25) $ 15,046 $ 1,751 $ 62,546 Brookfield Investment Mgmt 9,457 304 0 3,006 Center Coast Capital 3,717 344 0 0 Energy Income Partners 6,190 505 0 2,727 Franklin Advisers 56,807 511 0 243 Norges Bank 623,837 565 0 0 Wellington Management $ 512,659 $ 1,728 $ 0 $ 121

PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Arkose Currently Has Limited Index Ownership Perspectives on Pro-Forma Index Ownership “GP” Investor Base “Midstream” Investor Base Institutional (Passive) 2% Institutional (Passive) 1% Retail 5%  Limited number of Midstream units and GP shares are currently held by passive / index investors  Among the indices that Midstream and GP are part of, only the Alerian AMZ and AMZI indices have meaningful investor following Sponsors / Insiders 59% Institutional (Active) 45% Institutional (Active) 35% Upstream / Insiders 53%  All members of the AMZ and AMZI indices are MLPs Bloomberg Relevance Rating Bloomberg Relevance Rating Index Index  As a result, passive investors focused on MLP strategies may be sellers should GP acquire Midstream Alerian Energy Infrastructure Index 1 Yorkville MLP General Partners 0 Cushing 30 MLP Index 1 American Energy Independence 0 Tortoise MLP Index 1 Cushing MLP Mkt Cap 0 J.P. Morgan iDex U.S. SMID Cap Energy 0 Solactive US Energy Infrastructure MLP 1  But, due to the limited index holdings of Midstream, we do not expect price pressure or meaninful “churn” from this class of investors Bloomberg State Index of Colorado 0 Alerian Natural Gas MLP 0 Yorkville MLP Infrastructure Universe 0 Yorkville MLP Gathering & Processing 0 Yorkville PTP Universe Price Index 0 Yorkville MLP Distribution Growth Leaders 0 Wells Fargo Securities MLP Index 0 Yorkville MLP Distribution GLA Idx TR 0 Source: Thomson Reuters as of 1Q 2018, Bloomberg Note: Bloomberg relevance rating based on Bloomberg client usage and scaled from 0 – 5 with 5 being the most widely used. 5 Top Indices Shareholder Composition S&P MLP Index1 S&P MLP Index1 Alerian MLP Index4 Alerian MLP Infrastructure Index2

PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Summary of Key Index Inclusion Criteria Current Structure and Limited Public Float Exclude Midstream and GP from Major Indices Criteria Description Midstream GP Pro Forma S&P Mid Cap 400 S&P Mid Cap 400 S&P 500 and $450mm-2.1bn, respectively) ?  Minimum of 250k shares traded in each of 6 months leading up to evaluation   Viability    Company ETFs, royalty trusts, ADRs and ADSs are excluded Russell 1000 Russell 2000 Russell 1000  Sorted into Russell 1000 (currently $3.4bn+) and 2000 (~$144mm - 3.4bn) based on market cap rank $170,000  No mention in index methodology Viability    Company  Companies that produce unrelated business taxable income (UBTI) and do not block UBTI to equity Source: S&P U.S. Indices Methodology March 2018; FTSE Russell Methodology March 2018, and SEC Brief Overview for Foreign Private Issuers Note: S&P also considers sector balance in indices. 6 Russell Market CapMinimum of $30mm LiquidityAverage daily dollar trading volume must be larger than global median; as of 2017 Reconstitution, this was Public FloatAt least 5.5% of the shares outstanding Financial No annual filing requirement mentioned, presumed 10-K filing necessary   US DomicileAsset, headquarters, incorporation, and most liquid listing test Characteristics Must trade on eligible U.S. exchange   Corporate governance structure is consistent with US practice??? Royalty trusts, LLCs, closed-end investment companies, BDCs, SPACs and limited partnerships are Eligibleexcluded holders Time Since IPO At least before quarterly rank day (typically 1 month before quarter end) S&P Market CapSorted into S&P 500, Mid Cap 400, and Small Cap 600 based on market cap test ($6.1bn+, $1.6bn-6.8bn, LiquidityAnnual dollar value traded > 1.0x float adjusted market cap Public FloatAt least 50% of the shares outstanding FinancialSum of last four consecutive quarters and most recent quarter GAAP (core) net income should be positive Files 10-K annual reports with SEC   US DomicileSubject to fixed assets and revenues test Characteristics Primary listing of common stock on an acceptable exchange   Corporate governance structure consistent with US practice??? EligibleNYSE or NASDAQ listed common equities; closed end funds, LPs, MLPs, LLCs, BDCs, mortgage REITs, Time Since IPO Public for at least 6-12 months

PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Considerations For Index Inclusion Expected Index Ownership of Arkose (GP + Midstream) If Added to Various Indices Illustrative Required Insider Selling to Meet S&P’s 50% Public Float Test Index as % of Avg. Constituent's Float Value of Arkose (GP + Midstream) Upstream Index $ 2,694 32 % S&P 400 8 % $ 681 Warburg Pincus Yorktown $ 3,757 44 % Management / Board Public S&P 600 6 % $ 511 $ 979 12 % $ 9 % $ 276 3 % Russell 2000 8 % $ 681 Management / Board 62 % Warburg Pincus % Upstream Source: Thomson, company filings, Bloomberg, S&P U.S. Indices Methodology March 2018; FTSE Russell Methodology March 2018, SEC Brief Overview for Foreign Private Issuers, and Bloomberg market data as of 15-May-2018 1 Yorktown excluded because position is not large enough to fully exit and still pass public float test. 7 $ 486 million of required selling to meet S&P’s 50% public float test % of Holdings 51 18 % Based on current combined equity value, Arkose GP + Midstream could qualify based on size for the S&P 500 and Russell 1000 (though important criteria like C-Corp structure and % public float are not met) Required Selling as %of Holdings1 Russell 10003 %$ 255 S&P 50012 %$ 1,021

PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Simplification Trends Have Tended to Reduce Exposure to MLPs/K-1s and Increase Exposure to C-Corp/1099 Markets Sizing the Total Universe     There are ~100 publicly traded Energy MLPs Total market cap of Energy MLPs is $376bn 505 investors have positions in Alerian Index companies Top 20 Alerian Index Investors have a combined $2.2 trillion in equity AUM  There are ~85 Energy companies in the S&P 1500 (400, 500, 600 Indices) Total market cap of Energy companies in the S&P 1500 is $1.4 trillion 3,668 investors have positions in Energy companies in the S&P 1500 Top 20 investors of Energy companies have a combined $7.4 trillion in equity AUM    Shareholder Ownership Breakdown MLPs: Significant Insider and Retail Holdings C-Corp Energy: Greater Float and Institutional Holdings¹ Insider 2% Insider 17% Retail 16% Inst. 50% Retail 50% lnst. 84% Float 83% Float 98% Top 20 Alerian Index Investors Top 20 S&P 500 Energy Investors Depth in Largest Investors Pos. ($mm) Pos. ($mm) Pos. ($mm) Pos. ($mm) Investor Investor Investor Investor Invesco 6,072 OFI SteelPath 6,142 Cushing 1,723 Wellington 20,885 Capital World 20,875 Barrow, Hanley 5,667 Kayne Anderson 4,842 Neuberger Berman 1,454 GSAM 4,742 Eagle Global 1,197 Norges Bank 12,311 Franklin Advisers 5,474 T. Rowe Price 11,623 Capital International 5,179 Center Coast 2,776 OppenheimerFunds 839 JP Morgan AM 11,118 American Century 5,109 Dodge & Cox 10,191 First Eagle 5,033 Energy Income 2,382 MFS 720 Nuveen / TIAA-CREF 8,849 AllianceBernstein 4,853 Chickasaw Capital 2,200 Duff & Phelps 700 BlackRock (UK) 7,870 Boston Partners 4,542 Advisory Research 2,131 Westwood 634 Source: Bloomberg, Dealogic, Thomson Reuters as of 4Q 2017 Note: Blue shading denotes overlap between top MLP / Energy C-Corp investors ¹Includes average of Energy companies in the S&P 500. 8 ClearBridge 2,885 Miller/Howard 886 Capital Research 16,315 ClearBridge 5,585 Harvest Fund 5,529 Fidelity 1,634 Tortoise $ 9,286 Salient Capital $ 2,074 Fidelity $ 21,721 BlackRock $ 6,237 MLP C-CORP / UP-C

PRELIMINARY CONFIDENTIAL DRAFT – FOR DISCUSSION PURPOSES ONLY Illustrative Combined Shareholder Analysis Status Quo Illustrative Combination of Current Market Value Institutional (Active) 45% Upstream / Sponsors / Insiders 53% Top Active Holders % O/S Top Active Holders % O/S Retail 2% Institutional (Active) 41% Institutiona (Passive) 2% Tinicum 1.8 Tinicum Bank of America 2.2 1.2 FPR Partners Eagle Global CIBC Atlantic Trust 1.3 0.9 0.9 Retail 5% Institutional (Active) 35% Top Active Holders % O/S Bank of America UBS Yale University Alyeska Ostrum Asset Mgmt 0.7 0.6 0.6 0.6 0.6 Upstream / Sponsors / Insiders¹ 56% FPR Partners 3.2 Institutional (Passive) 2% Alyeska 1.6 Sponsors / Insiders 59% Institutional (Passive) 1% Eagle Global Tinicum JP Morgan 1.2 1.2 1.1 Deutsche JP Morgan 0.4 0.4 Blue shading indicates dedicated midstream investors Source: Thomson ownership as of Q1 ’18, subsequent 13D / G filings, and Bloomberg market data as of 15-May-2018 Note: Blue shading denotes MLP dedicated funds. 1 Includes assumed conversion of Series B units into ~4 million common GP shares based on status quo Series B conversion mechanics. 9 GP Common Shareholders Midstream Unitholders Advisory Research0.4 Dedicated midstream: 41% of Institutions 15% of outstanding Cushing Asset Mgmt1.5 Cushing Asset Mgmt0.6 Morgan Stanley0.5 Duff & Phelps0.5 Dedicated midstream: 56% of Institutions 24% of outstanding ClearBridge0.4 Tortoise3.0 GSAM3.0 Cohen & Steers1.8 OFI SteelPath3.8 % Cohen & Steers0.8 Dedicated midstream: 62% of Institutions 29% of outstanding Chickasaw1.6 Salient1.4 l Tortoise4.8 % GSAM4.5 Neuberger Berman2.4 Alps2.2 OFI Steelpath2.0 Harvest2.0 Tortoise6.0 % GSAM5.6 Alps3.7 Neuberger Berman3.4 Harvest2.7 Chickasaw2.6 Salient2.3