  Synchrotron powder diffraction data were measured on various gas hydrates
prepared at different fugacities and recovered to low temperatures. The data
extend to sin {\theta}/{\lambda} values of at least 1.01 {\AA}-1, in some cases
up to 1.48 {\AA}-1, i.e. at least 3 times further in reciprocal space than the
best single crystal data obtained so far. Here the results of CO2-hydrate are
presented in detail. Structural information is obtained from Rietveld
refinements to unprecedented precision. All H-bonded O-O distances are found to
be close to 2.75-2.76 {\AA}, i.e. very close to the values in ice Ih;
differences between a hydrogenated and deuterated host lattice are
insignificant. Cage occupancies were obtained for the first time in free
refinements together with positional parameters of the guest molecule and their
atomic displacement parameters. There is good agreement between the
experimental cage occupancies and prediction results from CSMGem.
