Robert H. Goddard experimented with liquid oxygen and various liquid hydrocarbons, including gasoline and liquid propane as well as ether, as rocket fuel, under a grant by Clark University. He concluded that although oxygen and hydrogen possessed the greatest heat energy per unit mass, that liquid oxygen and liquid methane offered greatest heat value of combinations which could be used without considerable difficulty. But, he said, "the most practical combination appears to be liquid oxygen References: 17 .