<?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>0001012779</rptOwnerCik>
            <rptOwnerName>DAVIS WILLIAM 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>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>26534.799</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2000.000</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Revocable Trust</value>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </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 13153.617 additional shares of common stock or common stock units.</footnote>
        <footnote id="F3">Includes dividends of 281.749 shares previously not reported pursuant to Rule 16a-11.</footnote>
        <footnote id="F4">Shares held by William L. Davis, not individually, but as trustee of the William L. Davis III Revocable Trust, or his successors in interest.   The reporting person is the trustee and settlor of the William L. Davis III Revocable Trust pursuant to the William L. Davis III Revocable Trust Agreement dated June 5, 1992, as amended.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>W. F. Schwind, Jr., Attorney-in-Fact for William L. Davis</signatureName>
        <signatureDate>2008-01-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2008-01-02
0
0000101778
MARATHON OIL CORP
MRO
0001012779
DAVIS WILLIAM L
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
26534.799
D
COMMON STOCK
2000.000
I
By Revocable Trust
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 13153.617 additional shares of common stock or common stock units.
Includes dividends of 281.749 shares previously not reported pursuant to Rule 16a-11.
Shares held by William L. Davis, not individually, but as trustee of the William L. Davis III Revocable Trust, or his successors in interest.   The reporting person is the trustee and settlor of the William L. Davis III Revocable Trust pursuant to the William L. Davis III Revocable Trust Agreement dated June 5, 1992, as amended.
W. F. Schwind, Jr., Attorney-in-Fact for William L. Davis
2008-01-04