Gasoline and fat are chemically similar in that they are essentially hydrocarbons, or chemical compounds that contain only carbon and hydrogen covlently bonded together. "Pure" gasoline is obtained by breaking down and distilling off lower boiling hydrocarbons from crude oil. Most of the hydrocarbon chemical compounds in gasoline have between 4 and 12 carbons that can be either a linear straight chain or branched configurations. Fats are composed of a central glycerol base with three different fatty acids attached to each of the glycerol oxygens. The fatty acids are composed of long linear chains of hydrocarbons that can vary in length depending on the fat.
In spite of this similarity, fats and gasoline are obviously different in terms of properties. Gasoline is a free flowing liquid with essentially no viscosity (it doesn't stick to the walls of a container). Fats are either oily liquids or soft solids depending on the degree of unsaturation of the fatty acid chains (in other words the number of carbon carbon double bonds present). Also, gasoline is obviously extremely flammable to the point of being explosive, whereas fats are simply flammable but pose no explosive danger.