To define the effect of common sedimentary minerals on pyrolysis of kerogen, previously separated and purified kerogen concentrates of alginite, amorphous liptinite and vitrinite were mixed with the following minerals: quartz, calcite, pyrite, limonite, kaolinite, bentonite and illite in various kerogen to mineral ratios. Rock Eval pyrolysis of these mixtures which contain 0.5 to 6.6% organic carbon show systematic variations in the parameters; hydrogen index, oxygen index, production index and Tmax and also in the amount of organic carbon consumed during the process. The variations for a given kerogen depend on the type of mineral and its proportion in the mixtures. The results of Rock Eval pyrolysis reflect the effect of the mineral matrix on the pyrolysis process of the sedimentary organic matter and its products. These effects are probably different from those caused by the same mineral during the natural oil and gas generation process. However, these analytical phenomena have to be recognized and accounted for in the interpretation of pyrolysis results.