<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
    <periodOfReport>2003-09-30</periodOfReport>
    <notSubjectToSection16>1</notSubjectToSection16>
    <issuer>
        <issuerCik>0000101778</issuerCik>
        <issuerName>MARATHON OIL CORP</issuerName>
        <issuerTradingSymbol>MRO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001238370</rptOwnerCik>
            <rptOwnerName>GOLDER G DAVID</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>MARATHON OIL CORP</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>Sr. V. P.-Commercial. and Dev.</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>
  <nonDerivativeTable>
   <nonDerivativeTransaction>
      <securityTitle>
          <value>COMMON STOCK</value>
      </securityTitle>
      <transactionDate>
          <value>2003-09-30</value>
      </transactionDate>
      <transactionCoding>
          <transactionFormType>4</transactionFormType>
          <transactionCode>D</transactionCode>
          <equitySwapInvolved>0</equitySwapInvolved>
      </transactionCoding>
      <transactionTimeliness>
      <value />
      </transactionTimeliness>
      <transactionAmounts>
          <transactionShares>
              <value>14400.000</value>
              <footnoteId id="F1" />
          </transactionShares>
          <transactionPricePerShare>
              <value>0</value>
          </transactionPricePerShare>
          <transactionAcquiredDisposedCode>
              <value>D</value>
          </transactionAcquiredDisposedCode>
      </transactionAmounts>
      <postTransactionAmounts>
          <sharesOwnedFollowingTransaction>
              <value>12932.000</value>
          </sharesOwnedFollowingTransaction>
      </postTransactionAmounts>
      <ownershipNature>
          <directOrIndirectOwnership>
              <value>D</value>
          </directOrIndirectOwnership>
      </ownershipNature>
   </nonDerivativeTransaction>
  </nonDerivativeTable>
  <derivativeTable>
  </derivativeTable>
<footnotes>
   <footnote id="F1">Forfeiture for no value of 6,800 shares of restricted stock granted under Marathon Oil Company's 1990 Stock Plan and 7,600 perfor
mance shares granted under Marathon Oil Corporation's 2003 Incentive Compensation Plan.</footnote>
</footnotes>
    <ownerSignature>
       <signatureName>By: R. J. Kolencik, Attorney-in-Fact for G. David Golder</signatureName>
       <signatureDate>2003-10-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0201
4
2003-09-30
1
0000101778
MARATHON OIL CORP
MRO
0001238370
GOLDER G DAVID
MARATHON OIL CORP
5555 SAN FELIPE ROAD
HOUSTON
TX
77056
0
1
0
0
Sr. V. P.-Commercial. and Dev.
COMMON STOCK
2003-09-30
4
D
0
14400.000
0
D
12932.000
D
Forfeiture for no value of 6,800 shares of restricted stock granted under Marathon Oil Company's 1990 Stock Plan and 7,600 perfor
mance shares granted under Marathon Oil Corporation's 2003 Incentive Compensation Plan.
By: R. J. Kolencik, Attorney-in-Fact for G. David Golder
2003-10-01