Gasoline probably will not kill the entire fire ant colony. Gasoline is highly repellent to ants and is likely to cause them to relocate. However, gasoline is dangerous to handle, and it kills any plant material it touches. Some of the residue remains in the soil and may leach or run off into ground and surface water.
Still more dangerous is the practice of treating a mound with gasoline and then setting it on fire. There have been instances where burning a fire ant mound has led to burning a house.
Find more information about fire ants in eXtension's Imported Fire Ant Resource Area.