Dry gas is an alcohol-based additive used in automobiles to prevent any water in the fuel from freezing, or to restore combustive power to gasoline spoiled by water. The name Drygas is actually a brand name, owned by Cristy. It is a liquid that is added into the fuel tank, that absorbs the water and keeps it in solution. Some brands contain methanol and some contain isopropyl alcohol.
Some states require a 10-15% ethanol solution be sold at refueling stations. Most current gasoline-powered automobiles can safely run up to a 15% ethanol solution without any modification. However, at 20% or above older vehicles may require replacing the fuel lines to prevent degradation and rupture, and the electric fuel pump may need modification to prevent ethanol "dry rot". There is no point in adding dry gas to fuel that already contains a significant percentage of ethanol, since ethanol is an alcohol.