In order to tackle emissions targets for CO2, there is increasing pressure to replace fossil fuels with renewable fuels. Biodiesel is one such renewable transportation fuel that comprises long-chain saturated fatty acid methyl esters such as methyl stearate. Although biodiesel has many advantages compared to conventional diesel, it suffers from poor performance at high pressures on account of crystallisation in fuel lines and in high-pressure injectors. We are currently investigating the crystallisation of biodiesel under low-temperature and high-pressure conditions, and are using methyl stearate as a model compound. The aim of the proposed experiment is to use high-pressure neutron powder diffraction to explore the phase behaviour of methyl stearate. This will contribute to the development of crystal-habit modifiers that prevent blockage of fuel lines under high-pressure conditions.