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EXHIBIT 21
<Table>
<Caption>
ENTITY JURISDICTION
898389 Alberta Ltd. Alberta
ACCROSERV SRL Barbados
ACCROVEN SRL Barbados
Alliance Canada Marketing L.P. Alberta
Alliance Canada Marketing LTD Alberta
Apco Argentina, Inc. Cayman Islands
Apco Properties Ltd. Cayman Islands
Arctic Fox Assets, L.L.C. Delaware
Aspen Products Pipeline LLC Delaware
Aux Sable Canada Ltd. Alberta
Aux Sable Canada LP Alberta
Aux Sable Liquid Products Inc. Delaware
Aux Sable Liquid Products LP Alberta
Bargath Inc. Colorado
Barrett Fuels Corporation Delaware
Barrett Resources International Corporation Delaware
Barrett Resources Peru Corporation Delaware
Baton Rouge Fractionators LLC Delaware
Baton Rouge Pipeline LLC Delaware
Beaver Dam Wash Energy, LLC Delaware
Beech Grove Processing Company Tennessee
Bison Royalty LLC Delaware
Black Marlin Pipeline Company Texas
Buccaneer Gas Pipeline Company, L.L.C. Delaware
Cannon Pipeline L.L.C. Oklahoma
Carbon County UCG, Inc. Delaware
Cardinal Operating Company Delaware
Cardinal Pipeline Company, LLC North Carolina
Castle Associates, L.P. Delaware
Chacahoula Natural Gas Storage, LLC Delaware
Choctaw Natural Gas Storage, LLC Delaware
ChoiceSeat, L.L.C. Delaware
Cross Bay Operating Company Delaware
Cross Bay Pipeline Company, L.L.C. Delaware
Cumberland Gas Pipeline Company Delaware
Cumberland Operating Company Delaware
Discovery Gas Transmission LLC Delaware
Discovery Producer Services LLC Delaware
Distributed Power Solutions L.L.C. Delaware
Dogwood Ventures Company, LLC Delaware
Eagle Gas Services, Inc. Ohio
</Table>
<Table>
E-Birchtree, LLC Delaware
EM&T NPC Co., LLC Delaware
Energy International Corporation Pennsylvania
Energy News Live, LLC Delaware
Energy Tech, Inc. Delaware
E-Oaktree, LLC Delaware
Erie & Hudson Development Company Ohio
ESPAGAS USA, Inc. Delaware
ESPAGAS, S.A. de C.V. Mexico
F T & T, Inc. Delaware
Fishhawk Ranch, Inc. Florida
FleetOne Inc. Delaware
FPT Marketing Company Limited Bermuda
Free Port Terminal Company Limited Bermuda
Fulton Energy Center, LLC Delaware
Garrison, L.L.C. Delaware
Gas Supply, L.L.C. Delaware
Georgia Strait Crossing Pipeline LP Utah
Goebel Gathering Company, L.L.C. Delaware
Great Basin Energy Resources, LLC Delaware
GSX Canada Limited Partnership British Columbia
GSX Operating Company, LLC Delaware
GSX Pipeline, LLC Delaware
GSX Western Pipeline Company Delaware
Gulf Liquids Holdings LLC Delaware
Gulf Liquids New River Project LLC Delaware
Gulf Star Deepwater Services, LLC Delaware
Gulf Stream Natural Gas System, L.L.C. Delaware
Gulfstream Management & Operating Services, L.L.C. Delaware
Halgas, Inc. Oklahoma
Hazleton Fuel Management Company Delaware
Hazleton Pipeline Company Delaware
HI-BOL Pipeline Company Delaware
Independence Operating Company Delaware
Independence Pipeline Company Delaware
Inland Ports, Inc. Tennessee
Juarez Pipeline Company Delaware
Kern River Acquisition, LLC Delaware
Kiowa Gas Storage, L.L.C. Delaware
Langside Limited Bermuda
Laughton, L.L.C. Delaware
Liberty Operating Company Delaware
Littlefield Energy, LLC Delaware
Longhorn Enterprises of Texas, Inc. Delaware
Longhorn Partners GP, L.L.C. Delaware
Longhorn Partners Pipeline, L.P. Delaware
</Table>
<Table>
Magnolia Methane Corp. Delaware
MAPCO Alaska Inc. Alaska
MAPCO Canada Energy Inc. Canada
MAPCO Energy Services, L.L.C. Delaware
MAPCO Impressions Inc. Oklahoma
MAPCO Inc. DE Delaware
MAPCO Indonesia Inc. Delaware
MAPL Investments, Inc. Delaware
Marsh Resources, Inc. Delaware
Memphis Generation, L.L.C. Delaware
Mid-Continent Fractionation and Storage, LLC Delaware
Millennium Energy Fund, L.L.C. Delaware
Moriche Bank Ltd. Barbados
Nebraska Energy, L.L.C. Kansas
NESP Supply Corp. Delaware
North Padre Island Spindown, Inc. Delaware
Northwest Alaskan Pipeline Company Delaware
Northwest Argentina Corporation Utah
Northwest Land Company Delaware
Northwest Pipeline Corporation Delaware
NWP Enterprises, Inc. Delaware
NWP Enterprises, LLC Delaware
Pacesetter/MVHC, Inc. Texas
Pan-Alberta Resources Inc. Canada
Parkco, L.L.C. Oklahoma
Parkco Two, L.L.C. Oklahoma
Petrolera Perez Companc Argentina
Piceance Production Holdings LLC Delaware
Pine Needle LNG Company, LLC North Carolina
Pine Needle Operating Company Delaware
Piper Power Company, LLC Delaware
Plains Petroleum Gathering Company Delaware
Rainbow Resources, Inc. Colorado
Realco of Crown Center, Inc. Delaware
Realco of San Antonio, Inc. Delaware
Realco Realty Corp. Delaware
Reserveco Inc. Delaware
Rio Vista Energy Marketing Company, L.L.C. Delaware
Rulison Gas Company, LLC Colorado
Rulison Production Company LLC Delaware
Servicios Williams International de Mexico S.A. de C.V. Mexico
Silver State Resources Management, LLC Delaware
Snow Goose Associates, L.L.C. Delaware
Sociedad Williams Enbridge y Compania Venezuela
Solutions EMT, Inc. Texas
SPV, L.L.C. Oklahoma
</Table>
<Table>
Tennessee Processing Company Delaware
Terrebonne Pipeline Company Delaware
TGPL Enterprises, Inc. Delaware
TGPL Enterprises, LLC Delaware
TGT Enterprises, Inc. Delaware
TGT Enterprises, LLC Delaware
The Tennessee Coal Company Delaware
Thermogas Energy, LLC Delaware
TM Cogeneration Company Delaware
Touchstar Energy Technologies, Inc. Texas
Touchstar Technologies Pty Ltd. South Africa
TouchStar Technologies, L.L.C. Delaware
TransCardinal Company Delaware
TransCarolina LNG Company Delaware
Transco Coal Gas Company Delaware
Transco Cross Bay Company Delaware
Transco Energy Company Delaware
Transco Energy Investment Company Delaware
Transco Energy Marketing Company Delaware
Transco Exploration Company Delaware
Transco Gas Company Delaware
Transco Independence Pipeline Company Delaware
Transco Liberty Pipeline Company Delaware
Transco P-S Company Delaware
Transco Resources, Inc. Delaware
Transco Terminal Company Delaware
Transco Tower Realty, Inc. Delaware
Transcontinental Gas Pipe Line Corporation Delaware
TransCumberland Pipeline Company Delaware
Transeastern Gas Pipeline Company, Inc. Delaware
TransNetwork Holding Company Delaware
Tulsa Williams Company Delaware
TXG Gas Marketing Company Delaware
Valley View Coal, Inc. Tennessee
Volunteer - Williams, L.L.C. Delaware
WCG NOTE CORP., INC. Delaware
WEM&T Trading GmbH Austria
WFS - Liquids Company Delaware
WFS - NGL Pipeline Company, Inc. Delaware
WFS - OCS Gathering Co. Delaware
WFS - Offshore Gathering Company Delaware
WFS - Pipeline Company Delaware
WFS Enterprises, Inc. Delaware
WFS Gathering Company, L.L.C. Delaware
WGP Enterprises, Inc. Delaware
WGP Gulfstream Pipeline Company, L.L.C. Delaware
</Table>
<Table>
WGP International Canada, Inc. New Brunswick
WHBC Holdings, LLC Delaware
WHBC, LLC Delaware
WHD Enterprises, Inc. Delaware
WHD Enterprises, LLC Delaware
Williams Acquisition Holding Company, Inc. (Del) Delaware
Williams Acquisition Holding Company, Inc. (NJ) New Jersey
Williams Aircraft, Inc. Delaware
Williams Alaska Air Cargo Properties, L.L.C. Alaska
Williams Alaska Petroleum, Inc. Alaska
Williams Alaska Pipeline Company, L.L.C. Delaware
Williams Alliance Canada Marketing, Inc. New Brunswick
Williams Arkoma Gathering Company, LLC Delaware
Williams Cove Point, Inc. Delaware
Williams Customer Information Solution, Inc. Delaware
Williams Distributed Power Services, Inc. Delaware
Williams EnergIa Espana, S.L. Spain
Williams Energia Italia SRL Italy
Williams Energy Canada Pipeline, Inc. New Brunswick
Williams Energy Canada, Inc. New Brunswick
Williams Energy Company Delaware
Williams Energy European Services Ltd. United Kingdom
Williams Energy Management LLC Delaware
Williams Energy Marketing & Trading Canada, Inc. New Brunswick
Williams Energy Marketing & Trading Europe Ltd England
Williams Energy Marketing & Trading Holdings UK Ltd. United Kingdom
Williams Energy Network, Inc. Delaware
Williams Energy Services, LLC Delaware
Williams Energy Solutions, Inc. Delaware
Williams Energy, L.L.C. Delaware
Williams Environmental Services Company Delaware
Williams Equities, Inc. Delaware
Williams Exploration Company Delaware
Williams Express, Inc. AK Alaska
Williams Express, Inc. Delaware
Williams Fertilizer, Inc. Delaware
Williams Field Services - Gulf Coast Company, L.P. Delaware
Williams Field Services - Matagorda Offshore Company, LLC Delaware
Williams Field Services Company Delaware
Williams Field Services Group, Inc Delaware
Williams Flexible Generation, LLC Delaware
Williams Gas Company Delaware
Williams Gas Energy, Inc. Delaware
Williams Gas Pipeline - Alliance Canada, Inc. Alberta
Williams Gas Pipeline - Alliance U.S., Inc. Delaware
Williams Gas Pipeline Company, LLC Delaware
</Table>
<Table>
Williams Gas Pipeline Mexico, S.A. de C.V. Mexico
Williams Gas Processing - Gulf Coast Company, L.P. Delaware
Williams Gas Processing - Mid-Continent Region Company Delaware
Williams Gas Processing - Wamsutter Company Delaware
Williams Gas Processing Company Delaware
Williams Gathering & Transportation, L.L.C. Oklahoma
Williams Generation Company - Hazleton Delaware
Williams Global Energy Cayman Limited Cayman Islands
Williams Global Holdings Company Delaware
Williams GmbH Austria
Williams GP LLC Delaware
Williams GSR, L.L.C. Delaware
Williams GSX Canada Inc. New Brunswick
Williams Gulf Coast Gathering Company, LLC Delaware
Williams Headquarters Acquisition Company Delaware
Williams Headquarters Building Company Delaware
Williams Headquarters Building, L.L.C. Delaware
Williams Headquarters Management Company Delaware
Williams Holdings GmbH Austria
Williams Hugoton Compression Services, Inc. Delaware
Williams Independence Marketing Company Delaware
Williams Indonesia, L.L.C. Delaware
Williams Information Technology, Inc. Delaware
Williams Intercontinental Holdings Company Delaware
Williams International Bermuda Limited Bermuda
Williams International Communications, Inc. Delaware
Williams International Company Delaware
Williams International Cusiana-Cupiagua Limited Cayman Islands
Williams International de Mexico, S.A. de C.V. Mexico
Williams International Ecuador Cayman Limited Cayman Islands
Williams International Ecuadorian Ventures Bermuda Limited Bermuda
Williams International El Furrial Limited Cayman Islands
Williams International Guara Limited Cayman Islands
Williams International Holdings Limited Cayman Islands
Williams International Investment Ventures Cayman Limited Cayman Islands
Williams International Investments Cayman Limited Cayman Islands
Williams International Jose Limited Cayman Islands
Williams International Oil & Gas Venezuela Limited Cayman Islands
Williams International Operations Ecuador Limited Cayman Islands
Williams International Operations Venezuela Limited Cayman Islands
Williams International Pigap Limited Cayman Islands
Williams International Pipeline Company Delaware
Williams International Services Company Nevada
Williams International Telecom Limited Delaware
Williams International Telecommunications Investments Cayman Limited Cayman Islands
Williams International Venezuela Limited Cayman Islands
</Table>
<Table>
Williams International Ventures Bermuda Ltd. Bermuda
Williams Learning Center, Inc. Delaware
Williams Lietuva Lithuania
Williams Lynxs Alaska CargoPort, L.L.C. Alaska
Williams Memphis Terminal, Inc. Delaware
Williams Merchant Services Company, Inc. Delaware
Williams Mid-South Pipelines, LLC Delaware
Williams Midstream Marketing and Risk Management, LLC Delaware
Williams Midstream Natural Gas Liquids, Inc. Delaware
Williams Mobile Bay Producer Services, L.L.C. Delaware
Williams Natural Gas Liquids Canada, Inc. Alberta
Williams Natural Gas Liquids, Inc. Delaware
Williams Natural Gas Storage, LLC Delaware
Williams New Soda, Inc. Delaware
Williams NGL, LLC Delaware
Williams Northern NGL Pipeline, L.L.C. Delaware
Williams Oil Gathering, L.L.C. Delaware
Williams Olefins Feedstock Pipelines, L.L.C. Delaware
Williams Olefins, L.L.C. Delaware
Williams One-Call Services, Inc. Delaware
WILLIAMS PETROLEOS ESPANA, S.L. Spain
Williams Petroleum Pipeline Systems, Inc. Delaware
Williams Petroleum Services, LLC Delaware
Williams Pipe Line Company, LLC Delaware
Williams Pipeline Services Company Delaware
Williams Pipelines Holdings, L.P. Delaware
Williams Portfolio Holdings, LLC Delaware
Williams Power Company, Inc. Delaware
Williams Production - Gulf Coast Company, L.P. Delaware
Williams Production Company, LLC Delaware
Williams Production Holdings LLC Delaware
Williams Production Mid-Continent Company Oklahoma
Williams Production RMT Company Delaware
Williams Production Rocky Mountain Company Delaware
Williams Refining & Marketing, L.L.C. Delaware
Williams Relocation Management, Inc. Delaware
Williams Resource Center, L.L.C. Delaware
Williams Risk Holdings, L.L.C. Delaware
Williams Risk Management L.L.C. Delaware
Williams Soda Holdings, LLC Delaware
Williams Sodium, LLC Delaware
Williams Sodium Products Company Delaware
Williams Strategic Sourcing Company Delaware
Williams Strategic Ventures, LLC Delaware
Williams Trading UK Ltd. United Kingdom
Williams TravelCenters, Inc. Delaware
</Table>
<Table>
Williams Underground Gas Storage Company Delaware
Williams Western Holding Company, Inc. Delaware
Williams Western Pipeline Company, LLC Delaware
Williams Wireless, Inc. Delaware
Williams WPC - I, Inc. Delaware
Williams WPC - II, Inc. Delaware
Williams WPC International Company Delaware
WilMart, Inc. Delaware
WilPro Energy Services El Furrial Limited Cayman Islands
WilPro Energy Services Pigap II Limited Cayman Islands
Worldwide Services Limited Cayman Islands
WPX Enterprises, Inc. Delaware
WPX Gas Resources Company Delaware
</Table>