welltotank

Well-to-tank (WTT) is a stage in life cycle assessment that accounts for the energy inputs and emissions involved in producing a fuel from resource extraction through processing, refining, and delivering it to a vehicle’s fuel tank. It covers the upstream activities required to make the fuel available at the pump.

It does not measure energy used during vehicle operation; that is the tank-to-wheels (TTW) or fuel-use phase. Together with TTW, WTT forms well-to-wheels (WTW), a common framework for comparing total energy use and greenhouse gas emissions across different fuels and propulsion systems.

The boundary of WTT varies by study but typically includes extraction, processing, refining, transport, and distribution to fueling stations. It may also encompass upstream electricity and heat used in processing, facility energy use, and emissions from non-combustion energy sources. How co-products are allocated (for example, ethanol and corn co-products) can significantly affect results.

WTT analyses rely on life cycle assessment methods and data models such as GREET (developed by Argonne National Laboratory). They are used in energy policy, fuel standards, and corporate sustainability reporting to compare fuels such as gasoline, diesel, biofuels, electricity, and hydrogen.

Limitations of WTT include dependence on data quality, regional energy mixes, allocation choices for co-products, and evolving technology. WTT does not capture end-use efficiency or non-energy environmental impacts beyond energy-related emissions, but it remains a fundamental component of broader well-to-wheels assessments.