The Environmental Protection Agency (EPA) is updating a portion of the Outer Continental Shelf (OCS) Air Regulations. Requirements applying to OCS sources located within 25 miles of states' seaward boundaries must be updated periodically to remain consistent with the requirements of the corresponding onshore area (COA), as mandated by the Clean Air Act. The portion of the OCS air regulations that is being updated pertains to the requirements for OCS sources for which Massachusetts is the designated COA. The Commonwealth of Massachusetts' requirements discussed in this document will be incorporated by reference into the Code of Federal Regulations and listed in the appendix to the Federal OCS air regulations.