Exhibit 21 SUBSIDIARIES OF RENTECH, INC. OKON, Inc., a Colorado corporation Petroleum Mud Logging, Inc., a Colorado corporation REN Testing Corporation, a Colorado corporation, doing business as Ren Corporation Rentech Development corporation, a Colorado corporation Rentech Services Corporation, a Colorado corporation We own 100% of the subsidiaries, except for REN Corporation, as to which we own 56%. The subsidiaries are included in our consolidated financial statements.