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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-02-28</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001357371</issuerCik>
        <issuerName>BreitBurn Energy Partners L.P.</issuerName>
        <issuerTradingSymbol>BBEP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001392016</rptOwnerCik>
            <rptOwnerName>Brown Gregory C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>515 SOUTH FLOWER STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 4800</rptOwnerStreet2>
            <rptOwnerCity>LOS ANGELES</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>90071</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Executive Vice President</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Performance Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-02-28</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>10373</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Units representing limited  partner interests</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>10373</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10373</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each Performance Unit is the economic equivalent of one common unit representing a limited partner interest (&quot;common unit&quot;) in BBEP and is accompanied by a distribution equivalent right, entitling the holder, immediately prior to settlement of the Performance Unit to an additional number of Performance Units based upon the relationship between the amount of distributions paid on a common unit during the period between the vesting commencement date and the settlement date of the Performance Unit and the market price of the common units prior to the payment of such distributions.  On the settlement date, the payment amount will be subject to adjustment by multiplying such payment amount by a factor of 0% to 200% depending on a comparison of the total return on a common unit relative to the total return on the securities of a competitive peer group of companies over a specified period of time.</footnote>
        <footnote id="F2">The Performance Units will be settled for cash or an equal number of common units, at the election of the reporting person, on the third anniversary of January 1, 2007.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Gregory C. Brown</signatureName>
        <signatureDate>2007-03-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
