We have measured the rates of evolution of the gases CO2, CO, H2, CH4 and the C2 and C3 hydrocarbons during the pyrolysis of seven Colorado oil shales. These shales yield from 9 to 61 gallons of oil per ton raw shale and are from various depths at two different sites. We used linear heating at a rate of 2supO/C/min for the retorting of all samples. This study was done to reveal the variations in gas evolution from shales with varying organic content and from varying stratigraphic and areal locations. We show comparisons between shales from each site and list some correlations of our data with data from Fischer assays. For the sake of comparison we include a sample of kerogen concentrate (mineral fraction removed by HCl-HF treatment) and a sample of retorted shale from a Fischer assay. We also test the ability of an existing kinetic model to predict our gas evolution results. Although the rate expressions are quite good, it is necessary to slightly modify some of the stoichiometric coefficients to obtain good agreement. The resulting kinetic model should adequately describe the gas and oil evolution behavior of shale from the upper portion of the Green River formation.