Geochemical data from 426 obsidian artifacts collected from a range of sites in the Southern Nasca Region (SNR), Peru highlight spatial and diachronic patterns in obsidian consumption. We compare source ascription data against different models of obsidian acquisition, and find that, for the most part, people adhered to a simple economic model where the most proximate source was exclusively used. Slight departures from this model during the Archaic, Early Nasca, and Tiza periods suggest obsidian was in some cases acquired through alternative means. For the Archaic period we attribute this to higher degrees of mobility where obsidian acquisition was embedded within other activities. For the Early Nasca and Tiza periods we attribute this to the development of alternative exchange relations within the south-central Peruvian region. We also examine differences in obsidian acquisition across SNR river valleys and by elevation, with greater source diversity occurring in the central valleys and at lower elevations. © 2009 Elsevier Ltd.