EXHIBIT 21

Matrix Service Company

Subsidiaries

Matrix Service Inc., an Oklahoma corporation

Matrix Service Canada ULC, an Alberta, Canada unlimited liability corporation

Matrix North American Construction, Inc., an Oklahoma corporation

Matrix North American Construction, Ltd., a Canadian corporation

Matrix SME Canada, Inc., a Delaware corporation

Matrix SME Canada ULC, a Nova Scotia, Canada unlimited liability corporation

Matrix PDM Engineering, Inc., a Delaware corporation

Matrix PDM, LLC, an Oklahoma limited liability corporation

Matrix Applied Technologies, Inc., a Delaware corporation

Matrix International Holding Company, Ltd., a British corporation

Matrix Applied Technologies, Ltd., a South Korean corporation

Matrix Applied Technologies, Pty. Ltd., an Australian corporation

Houston Interests, LLC, an Oklahoma limited liability corporation

Devco USA, LLC, an Oklahoma limited liability corporation

River Consulting, LLC, a Louisiana limited liability corporation

River Food Services, LLC, a Maryland limited liability corporation

S&R Technical Services, Inc., an Oklahoma corporation

Matrix Products and Services S. de R.L. de C.V., a Mexican limited liability variable stock corporation