It is partly due to quantum effects that hydrogen (and deuterium) exhibits a dramatic compressibility: in its fluid state, prior to freezing at room temperature at 5.5 GPa, it experiences a volume reduction by a factor of 3. This huge compressibility raises the interesting prospect of using a structural measurement of the fluid to sample the, intermolecular interaction potential across an extremely wide range of molecular separations. Such an experiment is now feasible, on deuterium, using newly developed gas loading techniques, and we propose to measure the structure of the fluid up to 5.5 GPa. This measurement would also provide a determination of the D-D molecular bondlength which is currently unknown above ambient pressure. Due to orientational disorder, this cannot be determined by conventional crystallographic means.