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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 CRsbQEOCiZyK3QgIH1GcGQ==

<SEC-DOCUMENT>0001209191-08-028382.txt : 20080507
<SEC-HEADER>0001209191-08-028382.hdr.sgml : 20080507
<ACCEPTANCE-DATETIME>20080507180230
ACCESSION NUMBER:		0001209191-08-028382
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20080506
FILED AS OF DATE:		20080507
DATE AS OF CHANGE:		20080507

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Pioneer Southwest Energy Partners L.P.
		CENTRAL INDEX KEY:			0001407463
		STANDARD INDUSTRIAL CLASSIFICATION:	CRUDE PETROLEUM & NATURAL GAS [1311]
		IRS NUMBER:				260388421
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		5205 N. O'CONNOR BLVD., SUITE 200
		CITY:			IRVING
		STATE:			TX
		ZIP:			75039
		BUSINESS PHONE:		(972) 444-9001

	MAIL ADDRESS:	
		STREET 1:		5205 N. O'CONNOR BLVD., SUITE 200
		CITY:			IRVING
		STATE:			TX
		ZIP:			75039

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			PIONEER NATURAL RESOURCES USA INC
		CENTRAL INDEX KEY:			0000846920
		STANDARD INDUSTRIAL CLASSIFICATION:	CRUDE PETROLEUM & NATURAL GAS [1311]
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-34032
		FILM NUMBER:		08811325

	BUSINESS ADDRESS:	
		STREET 1:		5205 NORTH O CONNOR BOULEVARD
		STREET 2:		1400 WILLIAMS SQUARE WEST
		CITY:			IRVING
		STATE:			TX
		ZIP:			75039
		BUSINESS PHONE:		9156834768

	MAIL ADDRESS:	
		STREET 1:		5205 NORTH OCONNOR BOULEVARD
		STREET 2:		1400 WILLIAMS SQUARE WEST
		CITY:			IRVING
		STATE:			TX
		ZIP:			75039

	FORMER NAME:	
		FORMER CONFORMED NAME:	MESA OPERATING CO
		DATE OF NAME CHANGE:	19940113

	FORMER NAME:	
		FORMER CONFORMED NAME:	MESA OPERATING LIMITED PARNERSHIP
		DATE OF NAME CHANGE:	19940113

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			PIONEER NATURAL RESOURCES CO
		CENTRAL INDEX KEY:			0001038357
		STANDARD INDUSTRIAL CLASSIFICATION:	CRUDE PETROLEUM & NATURAL GAS [1311]
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1206

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-34032
		FILM NUMBER:		08811326

	BUSINESS ADDRESS:	
		STREET 1:		200 WILLIAMS SQUARE WEST
		STREET 2:		5205 N OCONNOR BLVD
		CITY:			IRVING
		STATE:			TX
		ZIP:			75039
		BUSINESS PHONE:		9724449001

	MAIL ADDRESS:	
		STREET 1:		200 WILLIAMS SQUARE WEST
		STREET 2:		5205 N OCONNOR BLVD
		CITY:			IRVING
		STATE:			TX
		ZIP:			75039
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc4.xml
<DESCRIPTION>FORM 4 SUBMISSION
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-05-06</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001407463</issuerCik>
        <issuerName>Pioneer Southwest Energy Partners L.P.</issuerName>
        <issuerTradingSymbol>PSE</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001038357</rptOwnerCik>
            <rptOwnerName>PIONEER NATURAL RESOURCES CO</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>5205 N. O'CONNOR BLVD, SUITE 200</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>IRVING</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>75039</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Indirect Owner of Gen Partner</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000846920</rptOwnerCik>
            <rptOwnerName>PIONEER NATURAL RESOURCES USA INC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>5205 N. O'CONNOR BLVD., SUITE 200</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>IRVING</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>75039</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Direct Owner of Gen Partner</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Units</value>
            </securityTitle>
            <transactionDate>
                <value>2008-05-06</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>20521200</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>19.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>20521200</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The securities reported on this Form 4 are held directly by Pioneer Natural Resources USA, Inc. (&quot;Pioneer USA&quot;).  Pioneer USA is a wholly-owned subsidiary of Pioneer Natural Resources Company (&quot;Pioneer&quot;).  Pioneer is an indirect beneficial owner of the reported securities.  Pioneer USA is also a direct owner of the general partner of the Issuer.</footnote>
        <footnote id="F2">On May 6, 2008, in connection with the Issuer's initial public offering, Pioneer USA contributed a portion of its ownership interest in the operating company to the Issuer in exchange for the reported securities, all in accordance with the Contribution Agreement, dated May 6, 2008, by and among Pioneer USA, the general partner and the Issuer.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>By: Mark H. Kleinman, Vice President</signatureName>
        <signatureDate>2008-05-07</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>Mark H. Kleinman, Vice President</signatureName>
        <signatureDate>2008-05-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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