I use Kleen Diesel. It costs 17 bucks for a gallon from the local parts store. The directions state to add 5 ounces to every 30 gallons. It also states that one gallon treats up to 300 gallons. So I figure I get about 10 tanks of fuel out of the gallon. I don't measure it I just pour a splash in down the filler neck before i refill my tank. That way I know that it gets mixed up into the fuel. i have heard of people using additives from lucas and ams products but Diesel Kleen is redatively available from walmarts, miejers, any part store, and almost any place that sells diesel fuel. That is why I picked that brand. It may not be the best out there but it is the easiest to get ahold of.