EPA is partially approving some, and limitedly approving and limitedly disapproving other, revisions to the Billings/Laurel sulfur dioxide (SO2) State Implementation Plan (SIP) submitted by the State of Montana on July 29, 1998 and May 4, 2000. The May 4, 2000 SIP revision was submitted to satisfy earlier commitments made by the Governor. The intended effect of this action is to make federally enforceable those provisions that EPA is partially and limitedly approving, and to limitedly disapprove those provisions that are not fully approvable. EPA is taking this action under sections 110 and 179 of the Clean Air Act (Act).