The EU Commission's “Clean Power for Transport” initiative aims to break the EU's dependence on imported oil whilst promoting the use of alternative fuels to reduce greenhouse gas emissions. Among the options considered is the use of liquefied natural gas (LNG) as a substitute for diesel in long haul trucks. It is interesting to ask how the lifecycle greenhouse gas (GHG) emissions of LNG compare with conventional diesel fuel for this application.The LNG available in Europe is mainly imported. This paper considers the “well-to-tank” emissions of LNG from various production routes, including: gas production, treatment and liquefaction, shipping to Europe, terminal, distribution and refuelling operations. “Tank-to-Wheel” emissions are considered for a range of currently-available engine technologies of varying efficiency relative to diesel.If LNG is used in a direct-injection engine having the same efficiency as a diesel engine, the “well-to-wheel” GHG emissions are typically around 19% lower than conventional diesel, or around 17% lower than diesel containing 7% FAME (B7).Different sources of LNG may have higher or lower savings, depending on the efficiency of liquefaction and the shipping distance. In the best cases, the WtW reduction may be as high as 25%.Some natural gas engines in the market are significantly less efficient than diesel engines. GHG emissions increase with reducing engine efficiency and in some cases in some cases, the gas engine could have higher WtW emissions than an equivalent diesel engine.