The effect of the mineral matrix of Turkish Goynuk and Green River oil shales on the conversion of kerogen into organic material in pyrolysis reactions was investigated in this study. The conversion of kerogen to volatile organic material in pyrolysis reactions increased with increased reaction temperatures for the original and demineralized products of oil shales. Increasing the heating rate also caused greater kerogen conversion. It was found that pyrolysis reactions were catalyzed by alkaline earth metal cations in carbonates and inhibited by silicates. The inhibition effect of the silicates seemed to be greater than the catalytic effect of the carbonates in the pyrolysis reactions of the original Goynuk and Green River oil shales.