Inclusion of “Substantially Similar” Rulings

The notion of “substantially similar” is a key concept in the definition of appropriate fuel quality standards as mandated by the Clean Air Act. Even so, the EPA’s rulings on the appropriate scope of which fuels are deemed “substantially similar” to motor fuel employed in vehicles at the time of the enactment of the Act had not been heretofore included in the main regulatory text detailing fuel regulations (i.e. 40 CFR Part 80): rather they had been generally published separately in the Federal Register, without subsequent compilation into 40 CFR Part 80. All “sub sim” rulings have concerned Otto-cycle motor fuel (i.g. gasoline, gasonline-oxygenate blends).

One potentially useful change brought on by the adoption of the EPA’s proposed 40 CFR Part