Exhibit 99.5

Using a black ink pen, mark your votes with an X as shown inthis example. Please do not write outside the designated areas. X02WQ9CSpecial Meeting Proxy Card.IMPORTANT SPECIAL MEETING INFORMATION+A Proposals — The Board of Directors recommends that you vote FOR Proposals 1 and 2.C Authorized Signatures — This section must be completed for your vote to be counted. — Date and Sign BelowNOTE: Please sign as name appears hereon. Joint owners should each sign. When signing as attorney, executor, administrator, trustee, guardian, or custodian, please give full title as such.Date (mm/dd/yyyy) — Please print date below. Signature 1 — Please keep signature within the box. Signature 2 — Please keep signature within the box.B Non-Voting ItemsChange of Address — Please print new address below. Comments — Please print your comments below.In their discretion, the proxies are authorized to vote upon such other business as may properly come before the Special Meeting or any adjournment or postponement thereof.For Against Abstain1. To approve the Agreement and Plan of Merger, datedAugust 14, 2018, by and among Diamondback Energy, Inc.,Sidewinder Merger Sub Inc. and Energen Corporation (as itmay be amended from time to time, the “Merger Agreement”)For Against Abstain2. To approve, by a non-binding advisory vote, certaincompensation that may be paid or become payable toEnergen Corporation’s named executive officers that isbased on or otherwise relates to the merger contemplatedby the Merger Agreement.Electronic Voting InstructionsAvailable 24 hours a day, 7 days a week!Instead of mailing your proxy, you may choose one of the votingmethods outlined below to vote your proxy.VALIDATION DETAILS ARE LOCATED BELOW IN THE TITLE BAR.Proxies submitted by Internet or telephone must be received by11:59 p.m. Central Time on [_], 2018. ([_], 2018 forEmployee Savings Plan Participants)qIF YOU HAVE NOT VOTED VIA THE INTERNET OR TELEPHONE, FOLD ALONG THE PERFORATION, DETACH AND RETURN THE BOTTOM PORTION IN THE ENCLOSED ENVELOPE.qVote by Internet• Go to www.investorvote.com/EGN• Or scan the QR code with your smartphone• Follow the steps outlined on the secure websiteVote by telephone• Call toll free 1-800-652-VOTE (8683) within the USA, US territories &Canada on a touch tone telephone• Follow the instructions provided by the recorded message

.Proxy — ENERGEN CORPORATIONImportant notice regarding the Internet availability of proxy materials for the Special Meeting of Shareholders.The Proxy Statement, Notice of Meeting and Annual Report are available at:[_]NOTICE TO EMPLOYEE SAVINGS PLAN PARTICIPANTS. If you are a participant in the Energen Corporation EmployeeSavings Plan (the “Plan”) you have the right to direct the Trustee under the Plan how full shares of Energen Corporation’sCommon Stock allocable to your account under the Plan as of [_], 2018, should be voted at the Special Meeting ofShareholders of Energen Corporation. Energen Corporation’s stock transfer agent, Computershare, will forward yourinstructions to the Vanguard Fiduciary Trust Company, Trustee of the Plan. If directions are not received by the transfer agenton or before [_], 2018, you will be treated as directing the Plan’s Trustee to vote your shares in the same proportionas the shares for which the Trustee has received timely instructions from others who do vote.Special Meeting of Shareholders — [_], 2018THIS PROXY IS SOLICITED BY THE BOARD OF DIRECTORS OF THE COMPANYThe undersigned hereby appoints James T. McManus, II and John K. Molen, and each of them, with power to act without the other and with power ofsubstitution, as proxies and attorneys-in-fact and hereby authorizes them to represent and vote all the shares of Energen Corporation Common Stock whichthe undersigned is entitled to vote at the Special Meeting of Shareholders of Energen Corporation to be held [_], 2018, or at any adjournmentor postponement thereof, with all powers which the undersigned would possess if present at the Special Meeting, upon all matters that may properly comebefore the Special Meeting. This proxy will be voted in accordance with the specific indications on the other side. In the absence of suchindications, this proxy will be voted FOR Proposals 1 and 2. The proxies are authorized to vote in their discretion upon such other matters as mayproperly come before the Special Meeting or any adjournment or postponement thereof.(Continued and to be marked, dated and signed, on the other side)qIF YOU HAVE NOT VOTED VIA THE INTERNET OR TELEPHONE, FOLD ALONG THE PERFORATION, DETACH AND RETURN THE BOTTOM PORTION IN THE ENCLOSED ENVELOPE.q