Confusion sometimes arises when comparing the relative magnitudes of the energy density of oil and gas versus hydrogen. For clarification a link to the graph Hydrogen Specific Energy has been added.
As can be seen, the value depends on whether the measurement is volume or mass based, with hydrogen having the higher energy density per kilogram, but lower when measured per litre.
The Energy in Hydrogen
On a mass basis, hydrogen has nearly three times the energy content of gasoline—120 MJ/kg for hydrogen versus 44 MJ/kg for gasoline. On a volume basis, however, the situation is reversed; liquid hydrogen has a density of 8 MJ/L whereas gasoline has a density of 32 MJ/L, as shown in the figure comparing energy densities of fuels based on lower heating values.
[Ref.: https://www.energy.gov/eere/fuelcells/hydrogen-storage]
[Ref.: Courtesy of Department of Energy, Hydrogen and Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy (EERE) : https://www.energy.gov/eere/fuelcells/hydrogen-storage]
