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Debt
 9 Months Ended
Sep. 30, 2025
Debt Disclosure [Abstract]  
Debt Debt
MPLX’s outstanding borrowings consist of the following:
(In millions)September 30,
2025		December 31,
2024
MPLX LP:
MPLX Credit Agreement$— $— 
Fixed rate senior notes25,969 21,158 
Consolidated subsidiaries:
MarkWest— 11 
ANDX31 31 
Finance lease obligations7 6 
Total26,007 21,206 
Unamortized debt issuance costs(179)(126)
Unamortized discount(182)(132)
Amounts due within one year(1,501)(1,693)
Total long-term debt due after one year$24,145 $19,255 
Credit Agreement
MPLX’s credit agreement (the “MPLX Credit Agreement”) matures in July 2027 and, among other things, provides for a $2.0 billion unsecured revolving credit facility and letter of credit issuing capacity under the facility of up to $150 million. Letter of credit issuing capacity is included in, not in addition to, the $2.0 billion borrowing capacity. Borrowings under the MPLX Credit Agreement bear interest, at MPLX’s election, at either the Adjusted Term SOFR or the Alternate Base Rate, both as defined in the MPLX Credit Agreement, plus an applicable margin.
During the nine months ended September 30, 2025, MPLX borrowed $106 million under the MPLX Credit Agreement, at a weighted average interest rate of 7.740 percent, and repaid $106 million of these borrowings. At September 30, 2025, MPLX had no outstanding borrowings and less than $1 million in letters of credit outstanding under this facility, resulting in total availability of approximately $2.0 billion or approximately 100 percent of the borrowing capacity.
Fixed Rate Senior Notes
MPLX’s senior notes, including those issued by consolidated subsidiaries, consist of various series of senior notes maturing between 2026 and 2058 with interest rates ranging from 1.750 percent to 6.200 percent. Interest on each series of notes is payable semi-annually in arrears on various dates depending on the series of the notes.
The following table summarizes debt issuances during the nine months ended September 30, 2025, all of which were issued in an underwritten public offering:
Issue DateAggregate Principal Amount
(in millions)		Note(s)Coupon (percent)Price to Public
(percent of par)		Interest Payment DatesMaturity Date
March 10, 2025$1,000 
(1)
5.40099.398April 1 and October 1April 1, 2035
March 10, 20251,000 
(1)
5.95098.331April 1 and October 1April 1, 2055
August 11, 20251,250 
(2)
4.80099.880February 15 and August 15February 15, 2031
August 11, 2025750 
(2)
5.00098.936January 15 and July 15January 15, 2033
August 11, 20251,500 
(2)
5.40098.943March 15 and September 15September 15, 2035
August 11, 2025$1,000 
(2)
6.20098.277March 15 and September 15September 15, 2055
(1)    On April 9, 2025, MPLX used $1.2 billion of the net proceeds from the issuance of senior notes in March 2025 to redeem all of (i) MPLX’s outstanding $1,189 million aggregate principal amount of 4.875 percent senior notes due June 2025 and (ii) MarkWest’s outstanding $11 million aggregate principal amount of 4.875 percent senior notes due June 2025. MPLX intends to use the remaining net proceeds for general partnership purposes.
(2)    We used a portion of the net proceeds from this offering to fund the Northwind Midstream Acquisition, including the payment of related fees and expenses, and to increase cash and cash equivalents following the recently completed BANGL Acquisition and BANGL Debt Repayment. We intend to use the remainder of the net proceeds from this offering for general partnership purposes, which may include capital expenditures and other working capital requirements.
On February 18, 2025, MPLX repaid all of MPLX’s outstanding $500 million aggregate principal amount of 4.000 percent senior notes due February 2025 at maturity.
On July 3, 2025, MPLX used cash on hand to extinguish approximately $656 million principal amount of debt outstanding, including interest, related to certain term and revolving loans assumed as part of the BANGL Acquisition. See Note 3 for additional information on the BANGL Acquisition.