Graphite oxide (GO) and several of its derivatives have been studied using C-13 and H-1 NMR. The C-13 NMR lines at 60, 70 and 130 ppm have been re-assigned. The > C=C < double bonds are relatively stable in comparison with the C-O-C and C-O-H groups. There are at least two magnetically inequivalent C-O-H sites,land the structure does not necessarily possess long-range order. Water molecules interact very strongly with the structure. The results reveal a number of new structural features of graphite oxide.