EXHIBIT 21

Matrix Service Company

Subsidiaries

Matrix Service Inc., an Oklahoma corporation

Matrix Service Inc. Canada, an Ontario, Canada corporation

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

Matrix SME, Inc., an Oklahoma 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

Mobile Aquatic Solutions, Inc., an Oklahoma corporation