The first step in cleaning up a gas spill is to absorb it with a clay-type cat litter, sand, baking soda or a commercial absorbent. After the gas has been soaked up, contact a local fire department to find out the rules about disposing of this type of material because rules vary depending on the state.
Once the gas has been soaked up, the remainder of the stain can be treated with a paste of powdered dishwashing detergent and water. Scrub the stain, let the solution stand for several minutes and rinse with water. A solution of trisodium phosphate can be used to remove tougher stains.