It's the 10¢ fuel excise tax. This exemption was used in the past to kick-start the first-generation ethanol industry. Then it was replaced by a producer credit program, which does not exist. We could not really benefit from it, because we were really the second wave of the biofuels sector. Today the natural gas sector and the propane sector benefit from that exemption when they use their resources as a transportation fuel. Liquefied natural gas is an example.
On April 13th, 2017. See this statement in context.