Interplanar spacings (d values) from X-ray powder diffraction data occur over a wide range of values for the phases that have been described to date. They are not; however, uniformly distributed; rather, the d values are concentrated near certain values and thinly distributed in other regions, We have investigated the possibility of utilizing this distribution of d's to develop a search/ match method for phase identification. We found that there exist single d values that can be unique or almost unique to a certain phase. Also, the number of phases that could be uniquely characterized by single d's was increased by limiting the classes of compounds that were searched. The use of such characteristic d values resulted in a simpler search/match procedure.