NYSE: WES | NYSE: WGP westerngas.com INVESTOR RELATIONS JACK SPINKS Manager, Investor Relations 832 636 3738 FOURTH QUARTER AND FULL-YEAR 2018 REVIEW February 15, 2019

对于投资者和Unitholders的重要信息的前瞻性声明，本报告并不构成对购买任何证券的要约或任何投票或批准要约的征求。关于本文讨论的拟议交易，西气股份有限公司(“WGP”)向证券交易委员会(“委员会”)提交了一份表格S-4的登记声明，其中包括WGP的招股说明书和西气合伙人的委托书Lp(“WES”)。WES和WGP还可就拟议的交易向委员会提交其他文件。一份明确的委托书/招股说明书已于2019年1月28日邮寄给韦斯大学的会员。敦促WES的投资者和会员阅读委托书/招股说明书(包括所有修改和补充)以及与拟议交易有关的其他文件，因为这些文件载有关于拟议交易的重要信息。投资者及会员可透过委员会在http://www.sec.gov.的网站，免费索取委托书/招股章程及其他文件，内载有关WES及WGP的重要资料。WES和WGP向委员会提交的文件副本也可在其网址www.westerngas.com上免费索取，或与其投资者关系部联系，电话为832-636-6000。征集WES、WGP的参与者、其各自的普通合伙人及其各自的普通合伙人的董事和执行干事可被视为就拟议的交易向WES的单一会员征求委托书的参与者。关于WES董事和执行官员的信息载于韦斯2018年2月16日向欧盟委员会提交的10-K表格年度报告中。关于工作组董事和执行官员的资料载于工作组于2018年2月16日向委员会提交的关于表10-K的年度报告。关于委托书招标参与者的其他信息以及对其直接和间接利益的描述，按证券持有或其他方式列出，载于委托书/招股说明书和可能提交委员会的其他相关材料。这些文件的免费副本可通过上述联系方式获得。关于前瞻性陈述的警告声明本报告包含前瞻性陈述。例如，关于未来财务业绩、未来竞争定位的报表, 未来的市场需求、对单个投资者的未来利益、未来的经济和行业状况、拟议的交易(包括其收益、结果、效果和时机)以及交易是否和何时完成，都是联邦证券法意义上的前瞻性陈述。WES、WGP及其各自的一般合作伙伴认为，他们的期望是基于合理的假设。然而，不能保证这种期望将被证明是正确的。一些因素可能导致实际结果与本报告中所表示的预测、预期结果或其他预期大不相同。这些因素包括但不限于：WES的单一持有者未能批准拟议的交易；终止拟议交易的条件未得到满足的风险；未获得或在未预期的条件下获得拟议交易所需的监管批准的风险；宣布或完成拟议交易对业务关系可能产生的不良反应或变化；拟议交易的时间不确定；对拟议交易的竞争性反应；拟议交易产生的意外费用、收费或费用；未决或潜在诉讼的结果；无法留住关键人员；在拟议交易完成后，形式伙伴关系预期财务业绩的不确定性；以及一般经济和/或行业特定条件的任何变化。WES和WGP警告说，前面列出的因素并不是排他性的。有关这些和其他风险因素的其他信息载于韦斯和工作组最近提交的关于表10-K的年度报告、关于表10-Q的后续季度报告、关于表格8-K的最新报告以及委员会其他文件，可在委员会网站http://www.sec.gov.上查阅所有随后的书面和口头前瞻性陈述，包括WES，WGP，提议的交易或其他可归因于WES和WGP的事项，或任何代表他们行事的人，都被上述警告声明明确地限定为完整的。每一份前瞻性声明只在特定声明的日期进行说明。除法律规定外，WES、WGP及其各自的普通合伙人不承担公开更新或修改任何前瞻性声明的义务。a调整任何预测的经调整的EBITDA与业务活动提供的现金净额和净收入的对账，或预测调整后的营业收入毛利率, 没有提供，因为目前无法合理地获得或估计这类数额所需的物品。纽约证券交易所：韦斯，WGP 2

Simplification & Strategic Acquisition Transactions Transactions Expected to Close by End of 1Q19 PRO FORMA STRUCTURE Subject to WES Unitholder Vote on February 27th Anadarko Petroleum Corporation Public Term Loan Facility to Finance Acquisition Cash Consideration Unitholders NYSE: APC . Opportunistically term out $2B facility with public bonds 55.5% 44.5% . No equity needed to fund 2019 capital program Western Midstream Partners, LP 2% Subject to Closing, Western Gas Equity Partners, LP to Become NYSE: WES Western Midstream Partners, LP 98% . Common units will trade on NYSE under “WES” ticker symbol Western Gas Partners, LP1 Operating Assets 1) Western Gas Partners, LP will remain the borrower for all existing and future indebtedness and owner of all operating assets and equity interests. www.westerngas.com | NYSE: WES, WGP 3

Strong 2018 Performance 2018 2018 ($ in Millions) Guidance Actuals WES Adjusted EBITDA1 $1,175 - $1,225 $1,206 WES Total Capital Expenditures2 $1,350 - $1,450 $1,458 WES Maintenance Capital Expenditures $85 - $95 $91 WES 2018 Distribution Growth 1.5 cents/quarter 1.5 cents/quarter WGP 2018 Distribution Growth 12% 12% 1) A reconciliation of the Adjusted EBITDA range to net cash provided by operating activities and net income is not provided because the items necessary to estimate such amounts are not reasonably accessible or estimable at this time. 2) Includes equity investments and the acquisition of our interests in Whitethorn ($150.6 million) and Cactus II ($12.1 million), which are accounted for as acquisitions on the statement of cash flows, and excludes capitalized interest. www.westerngas.com | NYSE: WES, WGP 4

4Q18 vs 3Q18 Financial Performance ($ in Millions) 4Q18 3Q18 Adjusted EBITDA $347.5 $314.5 Total Capital Expenditures1 $321.8 $328.9 Maintenance Capital Expenditures $29.9 $23.8 Distributable Cash Flow $257.3 $248.2 Coverage Ratio 1.10x 1.08x 1) Total Capital Expenditures attributable to WES includes equity investments and acquisition capital less capitalized interest. www.westerngas.com | NYSE: WES, WGP 5

4Q18 vs 3Q18 Operational Performance 4Q18 3Q18 Key Drivers Natural Gas Throughput DJ Basin and Marcellus, partially (Bcf/d) 3.93 3.85 offset by Chipeta and Wyoming Adjusted Gross Margin for Natural Gas Assets ($/Mcf) $1.05 $1.03 Crude, NGL & Produced DBM Water growth Water Throughput (MBbls/d) 434 421 Adjusted Gross Margin for Springfield revenue recognition and Crude, NGL & Produced $2.19 $1.76 equity investment distribution timing Water Assets ($/Bbl) offset by DBM Water growth www.westerngas.com | NYSE: WES, WGP 6

Focused Investment in High-Growth Basins 2019E Capital Expenditures: 2019E Adjusted EBITDA: 2019E Coverage Ratio: $1.3 to $1.4 Billion $1.8 to $1.9 Billion Coverage Expansion DJ Basin Delaware Basin DJ Basin Delaware Basin 37% 54% 37% 40% Other 13% Other 3% Equity Investments Equity Investments 6% 10% Note: Delaware Basin 2019E Adjusted EBITDA includes distributions from, and 2019E Capital Expenditures includes contributions to, the following equity investments: Red Bluff Express Pipeline, Mi Vida and Bone Spring gas processing plants. www.westerngas.com | NYSE: WES, WGP 7

Delaware Basin: Efficient Three-Product Growth NEW MEXICO TEXAS Gas, Crude & Water Opportunity Set Ramsey LOVING CULBERSON WINKLER Scalable Mentone Infrastructure 5 MILES REEVES APC Leasehold WARD Gas Processing Plant Leverage Opportunistic Existing/Future Gas Gathering Lines PLANNED SYSTEM Third Party Deals Regional Oil Treating Facility CAPACITY BY YE19 Existing/Future Oil Pipelines 1.5 Bcf/d Gas Processing Existing/Future Water Pipelines 190+ MBOPD Oil Treating Note: Assumes close of midstream asset acquisition, expected 1Q19 900+ MBbl/d Produced-Water Disposal www.westerngas.com | NYSE: WES, WGP 8

Unchanged 2019 Outlook ($ in millions, includes full-year effect of assets to be acquired) 2019 Guidance Adjusted EBITDA1 $1,800 - $1,900 Total Capital Expenditures2,3 $1,300 - $1,400 Maintenance Capital Expenditures $110 - $120 WES Distribution Growth 1% - 2% WGP Distribution Growth 6% - 8% Annual Distribution Coverage Minimum 1.2x 1) A reconciliation of the Adjusted EBITDA range to net cash provided by operating activities and net income is not provided because the items necessary to estimate such amounts are not reasonably accessible or estimable at this time. 2) Includes equity investments. 3) Includes exercise of a 30% interest in Red Bluff Express Pipeline for an estimated total cost of $110 million. www.westerngas.com | NYSE: WES, WGP 9

Appendices www.westerngas.com | NYSE: WES, WGP 10

WES Non-GAAP Reconciliation “Adjusted EBITDA” WES defines Adjusted EBITDA as net income (loss) attributable to Western Gas Partners, LP, plus distributions from equity investments, non-cash equity-based compensation expense, interest expense, income tax expense, depreciation and amortization, impairments, and other expense (including lower of cost or market inventory adjustments recorded in cost of product), less gain (loss) on divestiture and other, net, income from equity investments, interest income, income tax benefit, and other income. Three Months Ended September 30, thousands December 31, 2018 2018 Reconciliation of Net income (loss) attributable to Western Gas Partners, LP to Adjusted EBITDA attributable to Western Gas Partners, LP Net income (loss) attributable to Western Gas Partners, LP $ 109,058 $ 154,646 Add: Distributions from equity investments 57,982 51,023 Non-cash equity-based compensation expense 1,480 1,548 Interest expense 52,345 47,991 Income tax expense — 1,517 Depreciation and amortization (1) 98,637 81,826 Impairments (1) 75,629 23,930 Other expense (1) 8,143 33 Less: Gain (loss) on divestiture and other, net 961 65 Equity income, net – affiliates 50,272 43,110 Interest income – affiliates 4,225 4,225 Other income (1) — 592 Income tax benefit 355 — Adjusted EBITDA attributable to Western Gas Partners, LP $ 347,461 $ 314,522 1) Includes WES’s 75% share of depreciation and amortization; impairments; other expense; and other income attributable to Chipeta. www.westerngas.com | NYSE: WES, WGP 11

WES Non-GAAP Reconciliation “Adjusted EBITDA” WES defines Adjusted EBITDA as net income (loss) attributable to Western Gas Partners, LP, plus distributions from equity investments, non-cash equity-based compensation expense, interest expense, income tax expense, depreciation and amortization, impairments, and other expense (including lower of cost or market inventory adjustments recorded in cost of product), less gain (loss) on divestiture and other, net, income from equity investments, interest income, income tax benefit, and other income. Year Ended December 31, 2018 thousands Reconciliation of Net income (loss) attributable to Western Gas Partners, LP to Adjusted EBITDA attributable to Western Gas Partners, LP Net income (loss) attributable to Western Gas Partners, LP $ 445,775 Add: Distributions from equity investments 169,906 Non-cash equity-based compensation expense 7,032 Interest expense 184,008 Income tax expense 3,301 Depreciation and amortization (1) 334,645 Impairments (1) 226,950 Other expense (1) 8,327 Less: Gain (loss) on divestiture and other, net 1,312 Equity income, net – affiliates 153,024 Interest income – affiliates 16,900 Other income (1) 2,592 Income tax benefit 355 Adjusted EBITDA attributable to Western Gas Partners, LP $ 1,205,761 1) Includes WES’s 75% share of depreciation and amortization; impairments; other expense; and other income attributable to Chipeta. www.westerngas.com | NYSE: WES, WGP 12

WES Non-GAAP Reconciliation “Adjusted EBITDA” WES defines Adjusted EBITDA as net income (loss) attributable to Western Gas Partners, LP, plus distributions from equity investments, non-cash equity-based compensation expense, interest expense, income tax expense, depreciation and amortization, impairments, and other expense (including lower of cost or market inventory adjustments recorded in cost of product), less gain (loss) on divestiture and other, net, income from equity investments, interest income, income tax benefit, and other income. Three Months Ended September 30, thousands December 31, 2018 2018 Reconciliation of Net cash provided by operating activities to Adjusted EBITDA attributable to Western Gas Partners, LP Net cash provided by operating activities $ 268,912 $ 236,811 Interest (income) expense, net 48,120 43,766 Uncontributed cash-based compensation awards (53) (55) Accretion and amortization of long-term obligations, net (1,259) (1,257) Current income tax (benefit) expense 233 (14) Other (income) expense, net (1) (408) (598) Distributions from equity investments in excess of cumulative earnings – affiliates 7,510 5,592 Changes in assets and liabilities: Accounts receivable, net (7,877) 57,535 Accounts and imbalance payables and accrued liabilities, net 24,632 (14,781) Other items, net 10,176 (9,379) Adjusted EBITDA attributable to noncontrolling interest (2,525) (3,098) Adjusted EBITDA attributable to Western Gas Partners, LP $ 347,461 $ 314,522 1) Excludes the non-cash loss on the interest-rate swaps of $8.0 million for the three months ended December 31, 2018.. www.westerngas.com | NYSE: WES, WGP 13

WES Non-GAAP Reconciliation “Adjusted EBITDA” WES defines Adjusted EBITDA as net income (loss) attributable to Western Gas Partners, LP, plus distributions from equity investments, non-cash equity-based compensation expense, interest expense, income tax expense, depreciation and amortization, impairments, and other expense (including lower of cost or market inventory adjustments recorded in cost of product), less gain (loss) on divestiture and other, net, income from equity investments, interest income, income tax benefit, and other income. Year Ended December 31, 2018 thousands Reconciliation of Net cash provided by operating activities to Adjusted EBITDA attributable to Western Gas Partners, LP Net cash provided by operating activities $ 1,020,634 Interest (income) expense, net 167,108 Uncontributed cash-based compensation awards 879 Accretion and amortization of long-term obligations, net (5,142) Current income tax (benefit) expense 480 Other (income) expense, net( 1) (3,017) Distributions from equity investments in excess of cumulative earnings – affiliates 25,607 Changes in assets and liabilities: Accounts receivable, net 56,667 Accounts and imbalance payables and accrued liabilities, net (30,722) Other items, net (13,873) Adjusted EBITDA attributable to noncontrolling interest (12,860) Adjusted EBITDA attributable to Western Gas Partners, LP $ 1,205,761 Cash flow information of Western Gas Partners, LP Net cash provided by operating activities $ 1,020,634 Net cash used in investing activities (1,459,798) Net cash provided by (used in) financing activities 450,798 1) Excludes the non-cash loss on the interest-rate swaps of $8.0 million for the three months ended December 31, 2018.. www.westerngas.com | NYSE: WES, WGP 14

WES Non-GAAP Reconciliation “Distributable Cash Flow” WES defines Distributable cash flow as Adjusted EBITDA, plus interest income and the net settlement amounts from the sale and/or purchase of natural gas, condensate and NGLs under WES’s commodity price swap agreements to the extent such amounts are not recognized as Adjusted EBITDA, less Service revenues – fee based recognized in Adjusted EBITDA (less than) in excess of customer billings, net cash paid (or to be paid) for interest expense (including amortization of deferred debt issuance costs originally paid in cash, offset by non-cash capitalized interest), maintenance capital expenditures, Series A Preferred unit distributions and income taxes. Three Months Ended September 30, thousands except Coverage ratio December 31, 2018 2018 Reconciliation of Net income (loss) attributable to Western Gas Partners, LP to Distributable cash flow and calculation of the Coverage ratio Net income (loss) attributable to Western Gas Partners, LP $ 109,058 $ 154,646 Add: Distributions from equity investments 57,982 51,023 Non-cash equity-based compensation expense 1,480 1,548 Income tax (benefit) expense (355) 1,517 Depreciation and amortization (1) 98,637 81,826 Impairments (1) 75,629 23,930 Above-market component of swap agreements with Anadarko 10,896 12,601 Other expense (1) 8,143 33 Less: Recognized Service revenues – fee based (less than) in excess of customer billings 14,045 4,397 Gain (loss) on divestiture and other, net 961 65 Equity income, net – affiliates 50,272 43,110 Cash paid for maintenance capital expenditures (1) 29,892 23,837 Capitalized interest 6,489 6,967 Cash paid for (reimbursement of) income taxes 2,495 — Other income (2) — 592 Distributable cash flow $ 257,316 $ 248,156 Distributions declared (2) Limited partners – common units $ 149,557 $ 147,268 General partner 85,230 82,971 Total $ 234,787 $ 230,239 Coverage ratio 1.10 x 1.08 x 1) Includes WES’s 75% share of depreciation and amortization; impairments; other expense; cash paid for maintenance capital expenditures; and other income attributable to Chipeta. 2) Reflects cash distributions of $0.980 per unit and $0.965 per unit declared for the three months ended December 31, 2018, and September 30, 2018, respectively. www.westerngas.com | NYSE: WES, WGP 15

WES Non-GAAP Reconciliation “Adjusted Gross Margin” WES defines Adjusted gross margin as total revenues and other (less reimbursements for electricity-related expenses recorded as revenue), less cost of product, plus distributions from equity investments, and excluding the noncontrolling interest owner’s proportionate share of revenue and cost of product. Three Months Ended September 30, thousands December 31, 2018 2018 Reconciliation of Operating income (loss) to Adjusted gross margin attributable to Western Gas Partners, LP Operating income (loss) $ 166,210 $ 200,321 Add: Distributions from equity investments 57,982 51,023 Operation and maintenance 114,518 111,359 General and administrative 17,072 14,467 Property and other taxes 7,844 10,954 Depreciation and amortization 99,349 82,553 Impairments 75,630 25,317 Less: Gain (loss) on divestiture and other, net 961 65 Equity income, net – affiliates 50,272 43,110 Reimbursed electricity-related charges recorded as revenues 16,441 17,455 Adjusted gross margin attributable to noncontrolling interest 3,525 3,803 Adjusted gross margin attributable to Western Gas Partners, LP $ 467,406 $ 431,561 Adjusted gross margin attributable to Western Gas Partners, LP for natural gas assets $ 379,892 $ 363,536 Adjusted gross margin for crude oil, NGLs and produced water assets 87,514 68,025 www.westerngas.com | NYSE: WES, WGP 16