<?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>0001238373</rptOwnerCik>
            <rptOwnerName>MATHENY KENNETH L</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.-Investor Rel./Public Aff.</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>7.000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>52970.154</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">On May 6, 2004, the reporting person filed a Form 4 with the SEC reporting the exercise of a stock appreciation right on May 4, 2004 using the highest fair market value of Marathon Oil Corporation common stock during the period from April 30 thru May 4, 2004, which was $34.15.  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 Kenneth L. Matheny</signatureName>
        <signatureDate>2004-05-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2004-05-13
0
0000101778
MARATHON OIL CORP
MRO
0001238373
MATHENY KENNETH L
C/O MARATHON OIL CORPORATION
5555 SAN FELIPE ROAD
HOUSTON
TX
77056
0
1
0
0
V.P.-Investor Rel./Public Aff.
COMMON STOCK
2004-05-13
4
J
0
7.000
17.00
A
52970.154
D
On May 6, 2004, the reporting person filed a Form 4 with the SEC reporting the exercise of a stock appreciation right on May 4, 2004 using the highest fair market value of Marathon Oil Corporation common stock during the period from April 30 thru May 4, 2004, which was $34.15.  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 Kenneth L. Matheny
2004-05-14