The present study was undertaken to determine the rate at which oil shale kerogen decomposes and to determine the composition of the pyrolyric products formed at 300 to 350 degrees C in a helium atmosphere at atmospheric pressure. A study of the thermal reaction at these low temperatures is important because of the current interest in the in situ retorting processes of converting oil shale to shale oil. During in situ retorting it may take long periods of heating to raise the temperature of the oil shale from ambient temperature to the final retorting temperature, thus thermal reactions or intermediate temperatures may become important. The present study was made to investigate some of the possible variables in the thermal behavior of the oil shale organic material as a function of time and temperature.