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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-03-04</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001173583</rptOwnerCik>
            <rptOwnerName>CAZALOT CLARENCE P 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>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President and CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2005-03-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>8700.000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>48.75</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>428152.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2005-03-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
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            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
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                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>423052.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2005-03-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
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            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>700.000</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
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        <nonDerivativeTransaction>
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                <transactionCode>S</transactionCode>
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                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            </transactionAmounts>
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            <ownershipNature>
                <directOrIndirectOwnership>
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        <nonDerivativeTransaction>
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                <value>COMMON STOCK</value>
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            <transactionDate>
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            <transactionCoding>
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                <transactionCode>S</transactionCode>
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                <value></value>
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                <transactionPricePerShare>
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                </transactionPricePerShare>
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            </transactionAmounts>
            <postTransactionAmounts>
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            <ownershipNature>
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        <nonDerivativeTransaction>
            <securityTitle>
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            <transactionDate>
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                <transactionCode>S</transactionCode>
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            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4200.000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>48.82</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>390452.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2005-03-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3000.000</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>387452.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2005-03-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>381252.000</value>
                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
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        <nonDerivativeTransaction>
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            <transactionCoding>
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                <transactionCode>S</transactionCode>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
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                </transactionShares>
                <transactionPricePerShare>
                    <value>48.85</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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            <ownershipNature>
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        <nonDerivativeTransaction>
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            <transactionCoding>
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            <transactionTimeliness>
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            <ownershipNature>
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        <nonDerivativeTransaction>
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            <transactionDate>
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        <nonDerivativeTransaction>
            <securityTitle>
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            <transactionDate>
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X0202
4
2005-03-04
0
0000101778
MARATHON OIL CORP
MRO
0001173583
CAZALOT CLARENCE P JR
C/O MARATHON OIL CORPORATION
5555 SAN FELIPE ROAD
HOUSTON
TX
77056
1
1
0
0
President and CEO
COMMON STOCK
2005-03-04
4
S
0
8700.000
48.75
D
428152.000
D
COMMON STOCK
2005-03-04
4
S
0
5100.000
48.76
D
423052.000
D
COMMON STOCK
2005-03-04
4
S
0
700.000
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D
422352.000
D
COMMON STOCK
2005-03-04
4
S
0
26400.000
48.80
D
395952.000
D
COMMON STOCK
2005-03-04
4
S
0
1300.000
48.81
D
394652.000
D
COMMON STOCK
2005-03-04
4
S
0
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D
390452.000
D
COMMON STOCK
2005-03-04
4
S
0
3000.000
48.83
D
387452.000
D
COMMON STOCK
2005-03-04
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S
0
6200.000
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D
381252.000
D
COMMON STOCK
2005-03-04
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S
0
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369952.000
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COMMON STOCK
2005-03-04
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368952.000
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COMMON STOCK
2005-03-04
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S
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367252.000
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COMMON STOCK
2005-03-04
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366552.000
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COMMON STOCK
2005-03-04
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S
0
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366152.000
D
COMMON STOCK
2005-03-04
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S
0
1900.000
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364252.000
D
COMMON STOCK
2005-03-04
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S
0
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D
363352.000
D
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2005-03-04
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S
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363052.000
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COMMON STOCK
2005-03-04
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S
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358452.000
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2005-03-04
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S
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356652.000
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2005-03-04
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S
0
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D
356052.000
D
COMMON STOCK
2005-03-04
4
S
0
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D
355552.000
D
COMMON STOCK
2005-03-04
4
S
0
2300.000
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D
353252.000
D
COMMON STOCK
2005-03-04
4
S
0
7500.000
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D
345752.000
D
R. J. Kolencik-Attorney-in-Fact for Clarence P. Cazalot, Jr.
2005-03-08