Other people consider that the whole idea of "the hydrogen economy" is flawed. Compressed hydrogen has an energy density of only 5.6 megajoules per liter. Robert Zubrin looks at the practical problems of using hydrogen as an energy storage medium in "Energy Victory: Winning the War on Terror by Breaking Free of Oil". He considers that hydrogen is a very poor form of storage, and that batteries, methanol or dimethyl ether would be better. This point is reiterated in "Beyond Oil and Gas: The Methanol Economy" and in David MacKay's book described below.