This paper presents the results of analysis of samples from 14 geologic sources of obsidian in New Mexico. Once this was accomplished, 26 obsidian artifacts from archaeological sites in Oklahoma and New Mexico were analyzed and their compositions compared to those from various Western sources. The artifact data have been combined with the results of analysis of 87 other obsidian artifacts from Oklahoma, west Texas, and New Mexico that had been previously reported. The analyses have demonstrated that, while most of the archaeological specimens are derived from the Jemez Mountains in New Mexico, some were obtained from SE Idaho and west-central Utah. This information indicates that exchange in the Southern Plains prior to A.C. 1450 had a N-S orientation, as shown by the Idaho and Utah obsidian. After A.C. 1450, the exchange patterns appear to have changed to an E--W orientation. At this time, obsidian from the Jemez Mountains in New Mexico became important to people living in the Southern Plains.