This is the comic I need to put up whenever someone makes an energy density argument to defend their favorite pet fuel. For whatever reason, one of the most common argument scientists or engineers in the field of energy make in favor or against any particular fuel is always about energy density. Ethanol's not as good as gasoline as it has lower energy density. Gasoline's not as good as diesel. Plants have a very low energy density so biofuels are dumb. Honestly, after net energy balance (something almost as useless) you hear this argument second most often. But that's only because as scientists its one of the only numbers they can grasp but its about as consequential to choosing a fuel as the color. If energy density really mattered, we'd only use uranium.