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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-01-02</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001181653</rptOwnerCik>
            <rptOwnerName>DABERKO DAVID A</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>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2008-01-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2035.831</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>61.40</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>30400.666</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Annual Non-Retainer Common Stock Award granted under Marathon Oil Corporation 2007 Incentive Compensation Plan. The annual non-retainer stock-based compensation represented by these common stock units are credited to an unfunded account and are payable in shares of common stock upon reporting person's retirement from the Board of Directors.</footnote>
        <footnote id="F2">On June 18, 2007, the common stock of Marathon Oil Corporation split 2-for-1 for holders of record on May 23, 2007, resulting in the reporting person's ownership, in the aggregate, of 14078.6 additional shares of common stock or common stock units.</footnote>
        <footnote id="F3">Includes dividends of 305.114 shares previously not reported pursuant to Rule 16a-11.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>W. F. Schwind, Jr., Attorney-in-Fact for David A. Daberko</signatureName>
        <signatureDate>2008-01-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2008-01-02
0
0000101778
MARATHON OIL CORP
MRO
0001181653
DABERKO DAVID A
C/O MARATHON OIL CORPORATION
5555 SAN FELIPE ROAD
HOUSTON
TX
77056
1
0
0
0
COMMON STOCK
2008-01-02
4
A
0
2035.831
61.40
A
30400.666
D
Annual Non-Retainer Common Stock Award granted under Marathon Oil Corporation 2007 Incentive Compensation Plan. The annual non-retainer stock-based compensation represented by these common stock units are credited to an unfunded account and are payable in shares of common stock upon reporting person's retirement from the Board of Directors.
On June 18, 2007, the common stock of Marathon Oil Corporation split 2-for-1 for holders of record on May 23, 2007, resulting in the reporting person's ownership, in the aggregate, of 14078.6 additional shares of common stock or common stock units.
Includes dividends of 305.114 shares previously not reported pursuant to Rule 16a-11.
W. F. Schwind, Jr., Attorney-in-Fact for David A. Daberko
2008-01-04