[RustyLugNut]

Fuel taxes include sales taxes. Then local, state and federal taxes are dumped on top of that. It is a unique commodity that has such strategic and widespread importance that it is taxed accordingly.

Diesel emission fluid (DEF) is an additive. It is taxed via common sales tax. You could not tax it as a fuel because it isn't. If the government decided to tax it at a rate commensurate with fuel, many other products would be open to such taxation. The uproar from lubricant, belt and tire manufacturers as well as the air freshener tree hanging from your mirror , just to name a few, would be tremendous.

This doesn't mean they won't tax it. It just means they may have a fight on their hands from a much larger group of people than they expected.

The volume of DEF sold is quite small in comparison to the over all volume of fuel. The Federal Government may not see it worth the fight.

I can say this much, if they do tax DEF to the same level as fuel there will be a large illegal market for the stuff. It isn't anything special. DEF labs will pop up in various out of the way places and designer DEF will be sold via secret hand signs and hidden in large Monster Energy Drink containers.