In order to improve energy supply diversity and reduce carbon dioxide emissions, sustainable bio-fuels are strongly supported by EU and other governments in the world. While the feedstock of biofuels has caused a debate on the issue of sustainability, the used cooking oil (UCO) has become a preferred feedstock for biodiesel manufacturers. However, intensive energy consumption in the trans-esterification process during the UCO biodiesel production has significantly compromised the carbon reduction potentials and increased the cost of the UCO biodiesel. Moreover, the yield of biodiesel is only ∼90% and the remaining ∼10% feedstock is wasted as by-product glycerol. Direct use of UCO in diesel engines is a way to maximize its carbon saving potentials. This paper, as part of the EPID (Environmental and Performance Impact of Direct use of used cooking oil in 44 tonne trucks under real world driving conditions) project, presents the life cycle analysis of Straight UCO (SUCO) in terms of CO2 and energy consumption, compared with the UCO biodiesel and petroleum diesel. The UK carbon calculator developed by UK Department for Transport was used for the calculations. The results show that SUCO renewable fuel can reduce the WTW carbon footprint by 98% compared to diesel and by 52% compared to the UCO biodiesel.