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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-01-03</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>2006-01-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1916.002</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>65.24</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10443.440</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1000.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Revocable Trust</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Annual Director Stock Awards granted under Marathon Oil Corporation 2003 Incentive Compensation Plan. The annual non-retainer stock-based compensation represented by these common stock units vest upon reporting person's retirement from the Board of Directors. Shares of common stock will be issued upon vesting of common stock units.</footnote>
        <footnote id="F2">Includes dividends of 161.746 shares previously not reported pursuant to Rule 16a-11.</footnote>
        <footnote id="F3">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>R. J. Kolencik, Attorney-in-Fact for William L. Davis</signatureName>
        <signatureDate>2006-01-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-01-03
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
2006-01-03
4
A
0
1916.002
65.24
A
10443.440
D
COMMON STOCK
1000.000
I
By Revocable Trust
Annual Director Stock Awards granted under Marathon Oil Corporation 2003 Incentive Compensation Plan. The annual non-retainer stock-based compensation represented by these common stock units vest upon reporting person's retirement from the Board of Directors. Shares of common stock will be issued upon vesting of common stock units.
Includes dividends of 161.746 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.
R. J. Kolencik, Attorney-in-Fact for William L. Davis
2006-01-05