Exhibit 21 LIST OF SIGNIFICANT SUBSIDIARIES Jurisdiction in which Subsidiary or Affiliate Incorporated or Organized Chicago Bridge & Iron Company B.V. The Netherlands Arabian CBI Ltd. Saudi Arabia Arabian CBI Tank Manufacturing Company Limited Saudi Arabia Arabian Gulf Material Supply Company Ltd. Cayman Islands CBI Construcciones S.A. Argentina CBI Constructors Pty. Ltd. Australia CBI Constructors Pty. Ltd. (PNG) New Guinea CBI Constructors S.A. (Proprietary) Limited South Africa CB&I Finance Company Limited Ireland CBI Holdings (U.K.) Limited United Kingdom CBI Constructors Limited United Kingdom CB&I John Brown Limited United Kingdom CB&I London Limited United Kingdom CBI (Malaysia) Sdn. Bhd. Malaysia CB&I Nigeria, Limited Nigeria CBI (Philippines) Inc. Philippines CBI Venezolana, S.A. Venezuela Chicago Bridge & Iron Company (Egypt) LLC Egypt CMP Holdings B.V. The Netherlands CB&I Europe B.V. The Netherlands Horton CBI, Limited Canada Horton Services, Inc. Canada Southern Tropic Material Supply Company, Ltd. Cayman Islands P.T. Chicago Bridge & Iron (1) Indonesia Chicago Bridge & Iron (Antilles) N.V. Netherland Antilles CBI Eastern Anstalt Liechtenstein Oasis Supply Company Anstalt Liechtenstein CB&I Hungary Holding LLC (CBI Hungary Kft) Hungary CBI Overseas, LLC Delaware Chicago Bridge & Iron Company Delaware CB&I Constructors, Inc. Texas CB&I Tyler Company Delaware CB&I Paddington Limited United Kingdom CB&I Woodlands L.L.C. Delaware Howe-Baker International, L.L.C. Delaware Howe-Baker Holdings, L.L.C. Delaware Howe-Baker Engineers, Ltd. Texas HBI Holdings, L.L.C. Delaware Matrix Engineering, Ltd. Texas Callidus Technologies, L.L.C. Oklahoma CBI Services, Inc. Delaware Morse Construction Group, Inc. Washington Chicago Bridge & Iron Company Illinois Asia Pacific Supply Co. Delaware CBI Caribe, Limited Delaware CBI Company Ltd. Delaware Constructora C.B.I. Limitada Chile Central Trading Company, Ltd. Delaware Chicago Bridge & Iron Company (Delaware) Delaware Lealand Finance Company B.V. The Netherlands (1) Unconsolidated affiliate In addition, Chicago Bridge & Iron Company N.V. has multiple other consolidated subsidiaries providing similar contracting services outside the United States, the number of which changes from time to time depending upon business opportunities and work locations.