<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2024-03-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000101778</issuerCik>
        <issuerName>MARATHON OIL CORP</issuerName>
        <issuerTradingSymbol>MRO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001239236</rptOwnerCik>
            <rptOwnerName>DEATON CHAD C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MARATHON OIL CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>990 TOWN &amp; COUNTRY BOULEVARD</rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77024</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2024-03-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>8130</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>108860.254</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Non-Retainer Annual Director Stock Unit Award granted under Marathon Oil Corporation 2019 Incentive Compensation Plan. These common stock units will vest on the earlier of March 1, 2025, or the reporting person's departure from the BOD, and be payable in shares of common stock.</footnote>
        <footnote id="F2">Includes dividends of 577.476 shares previously not reported pursuant to Rule 16a-11.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>John D. Montanti, Attorney-in-Fact for Chad C. Deaton</signatureName>
        <signatureDate>2024-03-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
[{"type": "4", "sequence": "1", "filename": "wk-form4_1709674222.xml", "description": "FORM 4", "secsgml_size_bytes": 3553}]
X0508
4
2024-03-01
0
0000101778
MARATHON OIL CORP
MRO
0001239236
DEATON CHAD C
C/O MARATHON OIL CORPORATION
990 TOWN & COUNTRY BOULEVARD
HOUSTON
TX
77024
1
0
0
0
0
Common Stock
2024-03-01
4
A
0
8130
0
A
108860.254
D
Non-Retainer Annual Director Stock Unit Award granted under Marathon Oil Corporation 2019 Incentive Compensation Plan. These common stock units will vest on the earlier of March 1, 2025, or the reporting person's departure from the BOD, and be payable in shares of common stock.
Includes dividends of 577.476 shares previously not reported pursuant to Rule 16a-11.
John D. Montanti, Attorney-in-Fact for Chad C. Deaton
2024-03-05