Sec Form 4 Filing - Mustang HoldCo II LLC @ WEX Inc. - 2017-08-14

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Mustang HoldCo II LLC 2. Issuer Name and Ticker or Trading Symbol WEX Inc. [ WEX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O WARBURG PINCUS LLC, 450 LEXINGTON AVENUE 3. Date of Earliest Transaction (MM/DD/YY) 08/14/2017 (Street) NEW YORK, NY10017 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock, $0.01 par value per share ("Common Stock") 08/14/2017 S 2,390,000 D ( 1 ) ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 ) $ 102.25 177,207 D ( 1 ) ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Director Reporting Owners Reporting Owner Name / Address Relationships 10% Owner Officer Other Mustang HoldCo II LLC C/O WARBURG PINCUS LLC 450 LEXINGTON AVENUE NEW YORK, NY10017 X WARBURG PINCUS PRIVATE EQUITY (LEXINGTON) XI-A, L.P. C/O WARBURG PINCUS LLC 450 LEXINGTON AVENUE NEW YORK, NY10017 X WP (LEXINGTON) HOLDINGS II, L.P. C/O WARBURG PINCUS LLC 450 LEXINGTON AVENUE NEW YORK, NY10017 X WARBURG PINCUS XI (LEXINGTON) PARTNERS-A, L.P. C/O WARBURG PINCUS LLC 450 LEXINGTON AVENUE NEW YORK, NY10017 X WARBURG PINCUS XI (E&P) PARTNERS-B, L.P. C/O WARBURG PINCUS LLC 450 LEXINGTON AVENUE NEW YORK, NY10017 X WP MUSTANG CO-INVEST LLC C/O WARBURG PINCUS LLC 450 LEXINGTON AVENUE NEW YORK, NY10017 X WP MUSTANG CO-INVEST-B L.P. C/O WARBURG PINCUS LLC 450 LEXINGTON AVENUE NEW YORK, NY10017 X WP MUSTANG CO-INVEST-C L.P. C/O WARBURG PINCUS LLC 450 LEXINGTON AVENUE NEW YORK, NY10017 X KAYE CHARLES R C/O WARBURG PINCUS LLC 450 LEXINGTON AVENUE NEW YORK, NY10017 X Landy Joseph P. C/O WARBURG PINCUS LLC 450 LEXINGTON AVENUE NEW YORK, NY10017 X Signatures MUSTANG HOLDCO II /s/ James Neary, President 08/15/2017 Signature of Reporting Person Date WP XI LEXINGTON-A By: WP E&P XI GP, its general partner ("GP"), By: WP E&P XI LLC, its GP, By: WPP E&P XI, its sole member, By: WP Partners II US, its managing member, By: WP & Company US, its GP, By: /s/ Robert B. Knauss, Authorized Signatory 08/15/2017 Signature of Reporting Person Date WP LEXINGTON II By: WP E&P XI GP, its GP, By: WP E&P XI LLC, its GP, By: WPP E&P XI, its sole member, By: WP Partners II US, its managing member, By: WP & Company US, its GP, By: /s/ Robert B. Knauss, Authorized Signatory 08/15/2017 Signature of Reporting Person Date WP XI LEXINGTON PARTNERS-A By: WP E&P XI GP, its GP, By: WP E&P XI LLC, its GP, By: WPP E&P XI, its sole member, By: WP Partners II US, its managing member, By: WP & Company US, its GP, By: /s/ Robert B. Knauss, Authorized Signatory 08/15/2017 Signature of Reporting Person Date WP XI E&P PARTNERS-B By: WP E&P XI GP, its GP, By: WP E&P XI LLC, its GP, By: WPP E&P XI, its sole member, By: WP Partners II US, its managing member, By: WP & Company US, its GP, By: /s/ Robert B. Knauss, Authorized Signatory 08/15/2017 Signature of Reporting Person Date WP CO-INVEST LLC By: WP E&P XI GP, its managing member, By: WP E&P XI LLC, its GP, By: WPP E&P XI, its sole member, By: WP Partners II US, its managing member, By: WP & Company US, its GP, By; /s/ Robert. B. Knauss, Authorized Signatory 08/15/2017 Signature of Reporting Person Date WP CO-INVEST-B By: WP Bermuda XI, its GP, By /s/ Robert B. Knauss, Authorised Signatory 08/15/2017 Signature of Reporting Person Date WP CO-INVEST-C By: WP Bermuda XI, its GP, By: /s/ Robert B. Knauss, Authorised Signatory 08/15/2017 Signature of Reporting Person Date CHARLES R. KAYE By: /s/ Robert B. Knauss, Attorney-in-Fact* 08/15/2017 Signature of Reporting Person Date JOSEPH P. LANDY By: /s/ Robert B. Knauss, Attorney-in-Fact* 08/15/2017 Signature of Reporting Person Date

Explanation of Responses:

( 1 )This Form 4 is being filed in connection with the sale of shares of Common Stock of WEX Inc. (the "Issuer") by Mustang HoldCo II LLC ("Mustang Holdco II"). ( 2 )The unitholders of Mustang Holdco II are Warburg Pincus Private Equity (Lexington) XI - A, L.P. ("WP XI Lexington-A"), WP (Lexington) Holdings II, L.P. ("WP Lexington II"), Warburg Pincus XI (Lexington) Partners - A, L.P. ("WP XI Lexington Partners-A"), Warburg Pincus XI (E&P) Partners - B, L.P. ("WP XI E&P Partners-B"), WP Mustang Co-Invest LLC ("WP Co-Invest LLC"), WP Mustang Co-Invest-B L.P. ("WP Co-Invest-B"), and WP Mustang Co-Invest-C L.P. ("WP Co-Invest-C"). ( 3 )WP Lexington II is the managing member of Mustang Holdco II. Warburg Pincus (E&P) XI, L.P. ("WP E&P XI GP") is (i) the general partner of WP XI Lexington-A, WP Lexington II, WP XI Lexington Partners-A, and WP XI E&P Partners-B, and (ii) the managing member of WP Co-Invest LLC. Warburg Pincus (E&P) XI LLC ("WP E&P XI LLC") is the general partner of WP E&P XI GP. Warburg Pincus Partners (E&P) XI LLC ("WPP E&P XI") is the sole member of WP E&P XI LLC. Warburg Pincus Partners II (US), L.P. ("WP Partners II US") is the managing member of WPP E&P XI. Warburg Pincus & Company US, LLC ("WP & Company US") is the general partner of WP Partners II US. Warburg Pincus LLC ("WP LLC") is the manager of WP XI Lexington-A, WP Lexington II, WP XI Lexington Partners-A, and WP XI E&P Partners-B. ( 4 )Warburg Pincus (Bermuda) XI, Ltd. ("WP Bermuda XI") is the general partner of WP Co-Invest-B and WP Co-Invest-C. Warburg Pincus Partners II (Cayman), L.P. ("WPP II Cayman") is the sole shareholder of WP Bermuda XI. Warburg Pincus (Bermuda) Private Equity GP Ltd. ("WP Bermuda GP") is the general partner of WPP II Cayman. Mustang Holdco II, WP XI Lexington-A, WP Lexington II, WP XI Lexington Partners-A, WP XI E&P Partners-B, WP Co-Invest LLC, WP Co-Invest-B, WP Co-Invest-C, WP E&P XI GP, WP E&P XI LLC, WPP E&P XI, WP Partners II US, WP & Company US, WP Bermuda XI, WPP II Cayman, WP Bermuda GP, and WP LLC are collectively referred to herein as the "Warburg Pincus Entities"). ( 5 )Charles R. Kaye and Joseph P. Landy are each the Managing Members of WP & Company US, the Co-Chairmen and sole Directors of WP Bermuda GP, and the Managing Members and Co-Chief Executive Officers of WP LLC and, as such, may be deemed to control each of the Warburg Pincus Entities. Messrs. Kaye and Landy disclaim beneficial ownership of all shares of Common Stock of the Issuer held by the Warburg Pincus Entities. Messrs. Kaye and Landy together with the Warburg Pincus Entities are collectively referred to herein as the "Warburg Pincus Reporting Persons". Information with respect to each of the Warburg Pincus Reporting Persons is given solely by such Warburg Pincus Reporting Person, and no Warburg Pincus Reporting Person has responsibility for the accuracy or completeness of information supplied by another Warburg Pincus Reporting Person. ( 6 )By reason of the provisions of Rule 16a-1 of the Exchange Act, the Warburg Pincus Reporting Persons may be deemed to be beneficial owners of the 177,207 shares of Common Stock of the Issuer held by Mustang Holdco II. The Warburg Pincus Reporting Persons disclaim beneficial ownership of such shares of Common Stock of the Issuer except to the extent of their direct pecuniary interest therein. As of the date of this filing, this Form 4 shall not be deemed an admission that any reporting person or any other person referred to herein is a beneficial owner of any securities of the Issuer for purposes of Se ction 16 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or for any other purpose, or that any reporting person or other person has an obligation to file this Form 4.

Remarks: (A) Solely for purposes of Section 16 of the Exchange Act, each of the Warburg Pincus Reporting Persons may be deemed directors-by-deputization by virtue of certain Warburg Pincus Reporting Persons' (and certain affiliates of WP LLC to whom shares of Common Stock of the Issuer are transferred) contractual right to appoint a director to the board of directors of the Issuer. As a result, the "Director" box is marked in Item 5 of this Form 4. (B) Due to the limitations on the number of Reporting Persons allowed on each Form 4, WP E&P XI GP, WP E&P XI LLC, WPP E&P XI, WP Partners II US, WP & Company US, WP Bermuda XI, WPP II Cayman, WP Bermuda GP, and WP LLC are filing a separate Form 4. (C) Entity names in the signature blocks have been abbreviated. Please refer to Notes (1), (2), (3), and (4) of this Form 4 for the complete legal name of such entities.*The Powers of Attorney given by each of Mr. Kaye and Mr. Landy were previously filed with the SEC on July 11, 2016 (with a revised filing date of July 12, 2016) as exhibits 99.2 and 99.3 to the statement on Schedule 13D filed by WP LLC with respect to the Issuer and are hereby incorporated by reference.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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