During the transition period prior to December 1, 1994, certified RFG may be put into tanks that contain conventional gasoline bottoms, as long as the tank is essentially filled with certified RFG gasoline on December 1, 1994, and the gasoline is properly sampled and tested and is in compliance with the RFG downstream standards. After December 1, 1994, the mixing of RFG and conventional gasoline is prohibited.

This question and answer was posted at Consolidated List of Reformulated Gasoline and Anti-Dumping Questions and Answers: July 1, 1994 through November 10, 1997 (PDF)(333 pp, 18.17 MB, EPA420-R-03-009, July 2003, About PDF)