The prices of ethanol (D6) and biomass-based diesel (D4) renewable identification number (RIN) credits—the compliance mechanism used for the Renewable Fuel Standard (RFS) program administered by the U.S. Environmental Protection Agency (EPA)—each fell by more than one third between September 1 and October 16, our data shows. As of October 16, biomass-based diesel RINs (D4 RINs) were $0.90, and ethanol RINs (D6 RINs) were $0.89; both prices were more than 40 cents lower than on September 1. D4 RIN prices have not been this low since 2020, when EPA granted several small refinery exemptions that reduced fuel blending requirements and RIN prices.