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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-06-10</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>2005-06-10</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>700.000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>51.58</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
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                    <value>45099.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2005-06-10</value>
            </transactionDate>
            <transactionCoding>
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                <transactionCode>S</transactionCode>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>200.000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>51.51</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
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            </transactionDate>
            <transactionCoding>
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                <transactionCode>S</transactionCode>
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            </transactionCoding>
            <transactionTimeliness>
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            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1600.000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>51.47</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>43299.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
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                <value></value>
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                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
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            </transactionAmounts>
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                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
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        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
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            </transactionDate>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
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                <value></value>
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                <transactionShares>
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                <transactionPricePerShare>
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                </transactionPricePerShare>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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            <ownershipNature>
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        <nonDerivativeTransaction>
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                <transactionCode>S</transactionCode>
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            <transactionTimeliness>
                <value></value>
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                <transactionShares>
                    <value>500.000</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>41199.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2005-06-10</value>
            </transactionDate>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
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            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>400.000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>51.59</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>40799.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2005-06-10</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>300.000</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
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        <nonDerivativeTransaction>
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            <transactionDate>
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            <transactionTimeliness>
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                <transactionShares>
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                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                <directOrIndirectOwnership>
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        <nonDerivativeTransaction>
            <securityTitle>
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            <transactionDate>
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            <transactionTimeliness>
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                <transactionPricePerShare>
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                <transactionCode>G</transactionCode>
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                <footnoteId id="F1"/>
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                <value></value>
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                    <value>3000.000</value>
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                <transactionPricePerShare>
                    <value>0</value>
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                    <value>D</value>
                </transactionAcquiredDisposedCode>
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                <sharesOwnedFollowingTransaction>
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                <directOrIndirectOwnership>
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            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Gift to Fidelity Charitable Gift Fund (501(c)(3)).</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>By: R. J. Kolencik, Attorney-in-Fact for Kenneth L. Matheny</signatureName>
        <signatureDate>2005-06-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2005-06-10
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
2005-06-10
4
S
0
700.000
51.58
D
45099.000
D
COMMON STOCK
2005-06-10
4
S
0
200.000
51.51
D
44899.000
D
COMMON STOCK
2005-06-10
4
S
0
1600.000
51.47
D
43299.000
D
COMMON STOCK
2005-06-10
4
S
0
1000.000
51.55
D
42299.000
D
COMMON STOCK
2005-06-10
4
S
0
600.000
51.54
D
41699.000
D
COMMON STOCK
2005-06-10
4
S
0
500.000
51.45
D
41199.000
D
COMMON STOCK
2005-06-10
4
S
0
400.000
51.59
D
40799.000
D
COMMON STOCK
2005-06-10
4
S
0
300.000
51.48
D
40499.000
D
COMMON STOCK
2005-06-10
4
S
0
1000.000
51.49
D
39499.000
D
COMMON STOCK
2005-06-10
4
S
0
402.000
51.50
D
39097.000
D
COMMON STOCK
2005-06-10
4
S
0
600.000
51.69
D
38497.000
D
COMMON STOCK
2005-06-10
4
S
0
800.000
51.65
D
37697.000
D
COMMON STOCK
2005-06-10
4
S
0
500.000
51.64
D
37197.000
D
COMMON STOCK
2005-06-10
4
S
0
1800.000
51.63
D
35397.000
D
COMMON STOCK
2005-06-10
4
S
0
3300.000
51.62
D
32097.000
D
COMMON STOCK
2005-06-10
4
S
0
300.000
51.61
D
31797.000
D
COMMON STOCK
2005-06-10
4
S
0
1400.000
51.60
D
30397.000
D
COMMON STOCK
2005-06-10
4
S
0
100.000
51.68
D
30297.000
D
COMMON STOCK
2005-06-10
4
S
0
200.000
51.70
D
30097.000
D
COMMON STOCK
2005-06-10
4
G
0
3000.000
0
D
27097.000
D
Gift to Fidelity Charitable Gift Fund (501(c)(3)).
By: R. J. Kolencik, Attorney-in-Fact for Kenneth L. Matheny
2005-06-14