Oxalyl chloride, which is a liquid at RT, forms a disordered phase (I) on cooling to 260 K. This phase is unstable with respect to an ordered phase (II) below 250 K, but in practice, phase I may be super-cooled to 2 K, and we have determined the crystal structure of both phases I and II at this temperature. When phase-II is warmed from 2 K up to the melting point its volume shows ideal Debye behaviour until 100 K. Above this temperature there is a departure from ideality, the deviation becoming progressively larger up to the II to I transition at 250 K. It appears that the sample is ¿preparing¿ to transform, possibly through enhanced, correlated whole-molecule vibrations. We aim to carry out PDF measurements to characterise the development of disorder in phase-II as it approaches the transition. PDF data will also be collected on phase-I with the aim of detecting local order.