Fundamental understanding of the structural changes occurring during hydrate formation and inhibition is important in the development of new strategies to control hydrates in flowlines and in inhibitor design. Neutron diffraction coupled with Empirical Potential Structure Refinement (EPSR) simulation has been used to determine the hydration structure around propane molecules before and during sII hydrate formation. The EPSR simulation results were generated by fitting neutron data (with H/D

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... opic substitution) obtained from the SANDALS diffractometer at ISIS. Using this combination of techniques, the structural transformations of water around propane can be studied during propane (sII) hydrate formation. The hydration structure was found to be different in the liquid phases of the partially formed propane hydrate compared to that before any hydrate formation. The effect of a kinetic hydrate inhibitor, poly-N-pyrrolidone on the hydration structure was also examined. No significant effect was observed on the water structure in the presence of this inhibitor.