Structure of assemblages of fish at 97 sites using 12 metrics was examined. Of 176 species known from Oklahoma, 118 were collected. Few species had a statewide distribution and most were limited to the eastern one-half of the state. Number of species in a collection was 2–28 with a mean of 15. In four of 12 indices analyzed, means for the Canadian River drainage were significantly lower than those of the Red River drainage. No significant difference existed between drainages of the Arkansas and Red rivers or the Arkansas and Canadian rivers. Comparing groups from west to east showed five of the 12 mean indices for the panhandle group were significantly less than those for the rest of the state. For north to south groups, means for two of the 12 indices for the southern group were significantly larger than means for the rest of the state and significantly larger than 75% of the state for three other indices. Principal-components analysis of standardized means of indices for geographical blocks indicated that areas of the state could be similar in structure of assemblage, although they may contain different species.