Fuel	Sources	Processes
Liquid petroleum fuels (gasoline, diesel, kerosene, jet fuel, bunker fuel)	Conventional oil fields (ground and shore-based). Non-conventional sources (tar sands)	Refining
Liquid synthetic fuels	Natural gas, coal	Gasification
Biodiesel	Oil seed crops	Esterification, hydrogenation
Ethanol	Grain crops	Saccharification and distillation
	Sugar crops (cane)	Distillation
Advanced biodiesel	Biomass from crops or waste products	Gasification
Compressed natural gas (CNG)	Natural gas	Gasification
Electricity	Coal, gas, petroleum, nuclear, renewables (hydro, wind)	Electric generator (source dependent)
Hydrogen	Natural gas	Reforming, compression
	Electricity	Electrolysis
	Direct production using other sources	High temperature process

Source: adapted from IEA/OECD (2009) Transport, Energy and CO2: Moving toward sustainability. Paris: International Energy Agency.

Fuels Production Processes

Each fuel has specific sources and processes related to its transformation. The more marginal the sources and the more complex the processes, the higher the price and scarcity. A major challenge concerns the sustainability of the energy sources as well as of the processes leading to the creation of fuels that can be used by transportation.