We present the results of XRF analysis for 428 obsidian samples from archaeological sites in the Argentinian province of Mendoza and from central Chile. The archaeological samples come from different environments and have dates that range from 9000 to 300 bp. The results indicate that all known sources were utilized; however, the beginnings and the intensities of their exploitation were variable. On the contrary, strong differences appear, especially between the Cordilleran and the non-Cordillera sources. We suggest that this pattern is mainly related to differences in the accessibility, quality and abundance of the obsidian in the sources.