Sec Form 4 Filing - ARCLIGHT ENERGY PARTNERS FUND V, L.P. @ Third Coast Midstream, LLC - 2019-07-23

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

OMB APPROVAL OMB Number: 3235-0287 Expires: November 30, 2011 Estimated average burden hours per response... 0.5

1. Name and Address of Reporting Person ARCLIGHT ENERGY PARTNERS FUND V, L.P. 2. Issuer Name and Ticker or Trading Symbol Third Coast Midstream, LLC [ AMID] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) X __ Other (specify below) SEE REMARKS (Last) (First) (Middle) C/O ARCLIGHT CAPITAL PARTNERS, LLC, 200 CLARENDON STREET, 55TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 07/23/2019 (Street) BOSTON, MA02117 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 Units (limited partner interests) 07/23/2019 D 42,514,126 ( 1 ) D $ 0 0 ( 2 ) ( 3 ) ( 4 ) I See footnote ( 1 )

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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other ARCLIGHT ENERGY PARTNERS FUND V, L.P. C/O ARCLIGHT CAPITAL PARTNERS, LLC 200 CLARENDON STREET, 55TH FLOOR BOSTON, MA02117 X X SEE REMARKS Magnolia Infrastructure Holdings, LLC C/O ARCLIGHT CAPITAL PARTNERS, LLC 200 CLARENDON STREET, 55TH FLOOR BOSTON, MA02117 X X Magnolia Infrastructure Partners, LLC C/O ARCLIGHT CAPITAL PARTNERS, LLC 200 CLARENDON STREET, 55TH FLOOR BOSTON, MA02117 X X American Midstream GP, LLC C/O ARCLIGHT CAPITAL PARTNERS, LLC 200 CLARENDON STREET, 55TH FLOOR BOSTON,, MA02117 X X High Point Infrastructure Partners, LLC C/O ARCLIGHT CAPITAL PARTNERS, LLC 200 CLARENDON STREET, 55TH FLOOR BOSTON, MA02117 X X AMID GP Holdings, LLC C/O ARCLIGHT CAPITAL PARTNERS, LLC 200 CLARENDON STREET, 55TH FLOOR BOSTON, MA02117 X X ArcLight Capital Holdings, LLC C/O ARCLIGHT CAPITAL PARTNERS, LLC 200 CLARENDON STREET, 55TH FLOOR BOSTON, MA02117 X X ArcLight Capital Partners, LLC 200 CLARENDON STREET, 55TH FLOOR BOSTON, MA02117 X X Revers Daniel R C/O ARCLIGHT CAPITAL PARTNERS, LLC 200 CLARENDON STREET, 55TH FLOOR BOSTON, MA02117 X X Signatures /s/ Daniel R. Revers FUND V By: ArcLight PEF GP V, LLC, its General Partner By: ArcLight Capital Holdings, LLC, its Manager By: ACHP II, L.P., its Managing Member By: ACH GP, LLC, its General Partner By: Daniel R. Revers, Manager 07/24/2019 Signature of Reporting Person Date /s/ Daniel R. Revers, President MAGNOLIA INFRASTRUCTURE HOLDINGS, LLC By: Daniel R. Revers, President 07/24/2019 Signature of Reporting Person Date /s/ Daniel R. Revers MAGNOLIA INFRASTRUCTURE PARTNERS, LLC By: Daniel R. Revers, President 07/24/2019 Signature of Reporting Person Date /s/ Daniel R. Revers THIRD COAST MIDSTREAM HOLDINGS, LLC By: its Class A Member, 3CM Holdings, LLC By: Daniel R. Revers, President 07/24/2019 Signature of Reporting Person Date /s/ Daniel R. Revers 3CM HOLDINGS, LLC By: Daniel R. Revers, President 07/24/2019 Signature of Reporting Person Date /s/ Daniel R. Revers AMID GP HOLDINGS, LLC By: Daniel R. Revers, President 07/24/2019 Signature of Reporting Person Date /s/ Daniel R. Revers ARCLIGHT CAPITAL HOLDINGS, LLC By: ACHP II, L.P., its Managing Member By: ACH GP, LLC, its General Partner By: Daniel Revers, Manager 07/24/2019 Signature of Reporting Person Date /s/ Daniel R. Revers ARCLIGHT CAPITAL PARTNERS, LLC By: Daniel R. Revers, Managing Partner 07/24/2019 Signature of Reporting Person Date /s/ Daniel R. Revers 07/24/2019 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents common units representing limited partnership interests (the "Common Units") of Third Coast Midstream, LLC (f/k/a American Midstream Partners, LP), a Delaware limited liability company (the "Issuer"). ( 2 )Pursuant to that certain Master Contribution Agreement, dated July 22, 2019, by and among Anchor Midstream Acquisition, LLC, a Delaware limited liability company ("Anchor Acquisition"), 3CM Holdings, LLC (f/k/a High Point Infrastructure Partners, LLC), a Delaware limited liability company ("3CM"), Third Coast Midstream Holdings, LLC (f/k/a/ American Midstream GP, LLC), a Delaware limited liability company (the "General Partner"), Magnolia Infrastructure Holdings, LLC, a Delaware limited liability company ("Magnolia Holdings"), Magnolia Infrastructure Partners, LLC, a Delaware limited liability company ("Magnolia"), AMID GP Holdings, LLC, a Delaware limited liability company ("AMID GP"), JP Energy Development, L.P., a Delaware limited partnership ("JP Energy"), Busbar II, LLC, a Delaware limited liability company ("Busbar"), High Point Energy, LLC, a Texas limited liability company, ArcLight Energy Partners Fund V, L.P., ( 3 )(continued from footnote 2) a Delaware limited partnership ("Fund V"), Stephen W. Bergstrom, individually ("Bergstrom") and Daniel C. Campbell, individually, (i) JP Energy, as holder of 422,805 Common Units, transferred all of its Common Units to Magnolia Holdings, (ii) Magnolia Holdings, as holder of 20,372,720 Common Units, transferred all of its Common Units to the General Partner, (iii) Magnolia, as holder of 5,108,669 Common Units, transferred all of its Common Units to the General Partner, (iv) Busbar, as holder of 2,853,482 Common Units, transferred all of its Common Units to the General Partner and (v) Bergstrom, as holder of 64,221 Common Units, transferred all of his Common Units to the General Partner. Immediately following the preceding transactions, the General Partner, as holder of 41,209,117 Common Units, transferred all of its Common Units to Anchor Acquisition. ( 4 )On July 23, 2019, pursuant to a Plan of Conversion adopted by the Issuer, the Issuer converted into a Delaware limited liability company named "Third Coast Midstream, LLC" ("Third Coast Midstream" and, such conversion, the "AMID Conversion"). In connection with the AMID Conversion, each Common Unit issued and outstanding immediately prior to the AMID Conversion was converted into one limited liability company unit of Third Coast Midstream. Magnolia Holdings also beneficially owns 1,369,230 Common Units issuable upon exercise of the warrants issued to Magnolia Holdings by the Issuer, dated July 18, 2019. After the AMID Conversion, all of the outstanding warrants converted into the right to receive 1,369,230 limited liability company units of Third Coast Midstream. As a result of the AMID Conversion, all Common Units were cancelled and ceased to be outstanding and none of JP Energy, Magnolia Holdings, Magnolia and Busbar beneficially own any Common Units.

Remarks: (A) ArcLight Capital Holdings, LLC ("ArcLight Holdings") is the sole manager and member of ArcLight Capital Partners, LLC ("ArcLight Partners" and, together with ArcLight Holdings and Fund V, the "ArcLight Entities"). ArcLight Partners is the investment adviser to Fund V. ArcLight Holdings is the manager of the general partner of Fund V. Mr. Revers is a manager of ArcLight Holdings, and a managing partner of ArcLight Partners and has certain voting and dispositive rights as a member of ArcLight Partners' investment committee. Fund V directly owns Busbar and Magnolia Holdings, which owns Magnolia. Fund V, through Magnolia, also owns approximately 90% of the ownership interest in 3CM. 3CM and AMID GP, a subsidiary of Magnolia Holdings, own respectively, approximately 86% and 14% of the General Partner. (B) Some of the entity names in the signature blocks have been abbreviated due to the limitations of the electronic filing system. Please refer to the text above for the complete legal names of such entities.

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).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.