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

    <documentType>4</documentType><periodOfReport>2003-09-30</periodOfReport>
    <issuer>
        <issuerCik>0000778438</issuerCik>
        <issuerName>BERRY PETROLEUM CO</issuerName>
        <issuerTradingSymbol>BRY</issuerTradingSymbol></issuer><reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001094528</rptOwnerCik>
            <rptOwnerName>HAGG JOHN A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O BERRY PETROLEUM COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>5201 TRUXTUN AVE., SUITE 300</rptOwnerStreet2>
            <rptOwnerCity>BAKERSFIELD</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>93309</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector><isOfficer>0</isOfficer><isTenPercentOwner>0</isTenPercentOwner><isOther>0</isOther></reportingOwnerRelationship></reportingOwner><nonDerivativeTable><nonDerivativeHolding><securityTitle><value>Class A Common Stock</value></securityTitle><postTransactionAmounts><sharesOwnedFollowingTransaction><value>14000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></nonDerivativeHolding></nonDerivativeTable><derivativeTable><derivativeTransaction><securityTitle><value>Phantom Stock Units</value></securityTitle><conversionOrExercisePrice><value>0</value><footnoteId id="F1"/></conversionOrExercisePrice><transactionDate><value>2003-09-30</value></transactionDate><transactionCoding><transactionFormType>4</transactionFormType><transactionCode>A</transactionCode><equitySwapInvolved>0</equitySwapInvolved></transactionCoding><transactionAmounts><transactionShares><value>476</value></transactionShares><transactionPricePerShare><value>18.28</value></transactionPricePerShare><transactionAcquiredDisposedCode><value>A</value></transactionAcquiredDisposedCode></transactionAmounts><exerciseDate><value>1988-08-08</value><footnoteId id="F2"/></exerciseDate><expirationDate><value>1988-08-08</value><footnoteId id="F3"/></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>476</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>9282</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeTransaction><derivativeHolding><securityTitle><value>Non-Statutory Stock Option (NSO)</value></securityTitle><conversionOrExercisePrice><value>10.75</value></conversionOrExercisePrice><exerciseDate><value>1995-05-19</value></exerciseDate><expirationDate><value>2004-12-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>3000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>3000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Non-Statutory Stock Option (NSO)</value></securityTitle><conversionOrExercisePrice><value>10.625</value></conversionOrExercisePrice><exerciseDate><value>1995-12-02</value></exerciseDate><expirationDate><value>2005-12-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>3000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>3000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Non-Statutory Stock Option (NSO)</value></securityTitle><conversionOrExercisePrice><value>13.75</value></conversionOrExercisePrice><exerciseDate><value>1996-12-02</value></exerciseDate><expirationDate><value>2006-12-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>3000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>3000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Non-Statutory Stock Option (NSO)</value></securityTitle><conversionOrExercisePrice><value>18.94</value></conversionOrExercisePrice><exerciseDate><value>1998-05-15</value></exerciseDate><expirationDate><value>2007-12-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>5000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>5000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Non-Statutory Stock Option (NSO)</value></securityTitle><conversionOrExercisePrice><value>12.625</value></conversionOrExercisePrice><exerciseDate><value>1998-12-02</value></exerciseDate><expirationDate><value>2008-12-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>5000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>5000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Non-Statutory Stock Option (NSO)</value></securityTitle><conversionOrExercisePrice><value>14.0625</value></conversionOrExercisePrice><exerciseDate><value>1999-12-02</value></exerciseDate><expirationDate><value>2009-12-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>5000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>5000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Non-Statutory Stock Option (NSO)</value></securityTitle><conversionOrExercisePrice><value>15.69</value></conversionOrExercisePrice><exerciseDate><value>2000-12-02</value></exerciseDate><expirationDate><value>2010-12-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>5000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>5000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Non-Statutory Stock Option (NSO)</value></securityTitle><conversionOrExercisePrice><value>15.45</value></conversionOrExercisePrice><exerciseDate><value>2001-12-02</value></exerciseDate><expirationDate><value>2011-12-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>5000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>5000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding><derivativeHolding><securityTitle><value>Non-Statutory Stock Option (NSO)</value></securityTitle><conversionOrExercisePrice><value>16.14</value></conversionOrExercisePrice><exerciseDate><value>2002-12-02</value></exerciseDate><expirationDate><value>2012-12-02</value></expirationDate><underlyingSecurity><underlyingSecurityTitle><value>Class A Common Stock</value></underlyingSecurityTitle><underlyingSecurityShares><value>5000</value></underlyingSecurityShares></underlyingSecurity><postTransactionAmounts><sharesOwnedFollowingTransaction><value>5000</value></sharesOwnedFollowingTransaction></postTransactionAmounts><ownershipNature><directOrIndirectOwnership><value>D</value></directOrIndirectOwnership><natureOfOwnership><value/></natureOfOwnership></ownershipNature></derivativeHolding></derivativeTable><footnotes><footnote id="F1">1 for 1</footnote><footnote id="F2">Phantom Stock Units acquired under the Company's Non-Employee Director Deferred Stock and Compensation Plan in a transaction exempt under Rule 16b-3(c).  Shares are exercisable under the terms of the Plan upon resignation from the Board.</footnote><footnote id="F3">Phantom Stock Units acquired under the Company's Non-Employee Director Deferred Stock and Compensation Plan in a transaction exempt under Rule 16b-3(c).  Shares expire under the terms of the Plan upon resignation from the Board.</footnote></footnotes><remarks/><ownerSignature><signatureName>Kenneth A. Olson under POA for John A. Hagg</signatureName><signatureDate>2003-10-01</signatureDate></ownerSignature></ownershipDocument>

