Substantially Similar Interpretive Rules for Fuels and Fuel Additives Under the Clean Air Act

The term "substantially similar" is used in the Clean Air Act to distinguish which fuels and fuel additives are prohibited by EPA. There have been three interpretive rules published by EPA to address the definition of this term.

• 2008 Interpretive Rule for the term "Substantially Similar" (pdf) (160.63 KB, April 2008)
• 1991 Interpretive Rule for the term "Substantially Similar" (pdf) (254.74 KB, January 1991)
• 1981 Interpretive Rule for the term "Substantially Similar" (pdf) (41.58 KB, July 1981)