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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-05-13</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001238376</rptOwnerCik>
            <rptOwnerName>SCHWIND WILLIAM F JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MARATHON OIL CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>5555 SAN FELIPE ROAD</rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77056</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>V.P., General Counsel and Sec.</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2004-05-13</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>29.000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>31114.479</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">On May 3, 2004, the reporting person filed a Form 4 with the SEC reporting the exercise of a stock appreciation right on April 30, 2004 using the fair market value of Marathon Oil Corporation common stock on April 30, 2004,  which was $33.53.  That stock appreciation right was subject to adjustment to reflect the highest fair market value during the ten day trading period commencing April 30, 2004.  This Form 4 is being filed to reflect the number of shares the reporting person acquired based on the adjustment to reflect highest fair market value of Marathon Oil Corporation common stock during such ten day trading period, which was $34.50.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>By: R. J. Kolencik, Attorney-in-Fact for W. F. Schwind, Jr.</signatureName>
        <signatureDate>2004-05-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2004-05-13
0
0000101778
MARATHON OIL CORP
MRO
0001238376
SCHWIND WILLIAM F JR
C/O MARATHON OIL CORPORATION
5555 SAN FELIPE ROAD
HOUSTON
TX
77056
0
1
0
0
V.P., General Counsel and Sec.
COMMON STOCK
2004-05-13
4
J
0
29.000
17.00
A
31114.479
D
On May 3, 2004, the reporting person filed a Form 4 with the SEC reporting the exercise of a stock appreciation right on April 30, 2004 using the fair market value of Marathon Oil Corporation common stock on April 30, 2004,  which was $33.53.  That stock appreciation right was subject to adjustment to reflect the highest fair market value during the ten day trading period commencing April 30, 2004.  This Form 4 is being filed to reflect the number of shares the reporting person acquired based on the adjustment to reflect highest fair market value of Marathon Oil Corporation common stock during such ten day trading period, which was $34.50.
By: R. J. Kolencik, Attorney-in-Fact for W. F. Schwind, Jr.
2004-05-14