EXHIBIT 21.0

Subsidiaries of Registrant

Subsidiaries of

OREGON STEEL MILLS, INC.

Canadian National Steel Corporation –Alberta, Canada – dba Camrose Pipe Company Camrose Pipe Corporation– Delaware - dba Columbia Structural Tubing New CF&I, Inc. -Delaware (1) Oregon Steel de Guayana, Inc. - Delaware OSM GlassificationTM, Inc. - Oregon  CF&I Steel, L.P. (a partnership) – Delaware – dba Rocky Mountain Steel Mills (2) Colorado & Wyoming Railway Company – Delaware OSM Distribution, Inc. – Delaware Oregon Steel Mills Processing, Inc. – Delaware Oregon Feralloy Partners (a partnership) – Oregon (4) LSI Plate (a partnership) – Oregon (5)

| (1)                                                           | The Company owns 90% of New   CF&I, Inc.                                                                                                                                                                                                                           |
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| (2)                                                           | New CF&I, the general   partner of CF&I, owns 95.2% and 100% of the equity interest in CF&I   and Colorado & Wyoming Railway Company, respectively.  In addition, the Company directly owns   4.3% of the equity interest in CF&I, Steel L.P. |
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| (3)                                                           | The Company owns 60% of Oregon   Feralloy Partners.                                                                                                                                                                                                                    |
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| (4)                                                           | The Company Owns 50% of LSI   Plate.                                                                                                                                                                                                                                   |
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| The Company owns 100% of all   remaining subsidiaries listed. |