Given the environmental and social costs (e.g. climate change, local air pollution, resource depletion, vulnerability to supply shocks) associated with using fossil fuels in particular, taxing energy use is vital to help ensure that energy prices and use better reflect associated costs. Yet recent work shows inconsistencies - with no obvious rationale -in the taxation of different forms, uses and users of energy in many OECD countries when assessed against environmental and other social costs (OECD, 2013h). A full 33 out of 34 OECD countries tax diesel fuel at lower rates than gasoline, both in terms of energy and carbon content, the United States is the exception (Harding, 2014).