Oil and natural gas, coming from the decay of ancient oceans, are easier to use than coal but less available. Oil is especially valuable as the raw material for chemicals, including gasoline, synthetic fibers, and pharmaceuticals. Natural gas, recently cheaper because of fracking, produces less carbon dioxide per amount of heat than coal and oil. Yet natural gas is a more potent greenhouse, and its fugitive emissions of methane left unchecked counterbalances the lower carbon dioxide emissions.