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

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    <periodOfReport>2006-05-26</periodOfReport>

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

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        <reportingOwnerId>
            <rptOwnerCik>0001239300</rptOwnerCik>
            <rptOwnerName>HOWARD JERRY</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>
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            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Sr. V.P., Corporate Affairs</officerTitle>
        </reportingOwnerRelationship>
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            </transactionDate>
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                <footnoteId id="F1"/>
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                </transactionShares>
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                </transactionPricePerShare>
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                    <value>D</value>
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                    <value>55912.000</value>
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        <nonDerivativeTransaction>
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                <transactionPricePerShare>
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                </transactionAcquiredDisposedCode>
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                    <value>D</value>
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                    <value>D</value>
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                <value></value>
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                    <value>75.92</value>
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                    <value>D</value>
                </transactionAcquiredDisposedCode>
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        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Intra-plan fund transfer out of Marathon Oil Corporation common stock fund in Marathon Oil Company Thrift Plan.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Richard J. Kolencik, Attorney-in-Fact for Jerry Howard</signatureName>
        <signatureDate>2006-05-31</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-05-26
0
0000101778
MARATHON OIL CORP
MRO
0001239300
HOWARD JERRY
C/O MARATHON OIL CORPORATION
5555 SAN FELIPE ROAD
HOUSTON
TX
77056
0
1
0
0
Sr. V.P., Corporate Affairs
COMMON STOCK
2006-05-26
4
S
0
169.000
76.14
D
62712.000
D
COMMON STOCK
2006-05-26
4
S
0
200.000
76.10
D
62512.000
D
COMMON STOCK
2006-05-26
4
S
0
200.000
76.06
D
62312.000
D
COMMON STOCK
2006-05-26
4
S
0
500.000
76.02
D
61812.000
D
COMMON STOCK
2006-05-26
4
S
0
1900.000
76.01
D
59912.000
D
COMMON STOCK
2006-05-26
4
S
0
4000.000
76.00
D
55912.000
D
COMMON STOCK
2006-05-26
4
S
0
400.000
75.99
D
55512.000
D
COMMON STOCK
2006-05-26
4
S
0
900.000
75.98
D
54612.000
D
COMMON STOCK
2006-05-26
4
S
0
3100.000
75.97
D
51512.000
D
COMMON STOCK
2006-05-26
4
S
0
300.000
75.95
D
51212.000
D
COMMON STOCK
2006-05-26
4
S
0
3300.000
75.92
D
47912.000
D
Intra-plan fund transfer out of Marathon Oil Corporation common stock fund in Marathon Oil Company Thrift Plan.
Richard J. Kolencik, Attorney-in-Fact for Jerry Howard
2006-05-31