The isothermal decomposition of a New Albany oil shale has been studied in the temperature range of 375/sup 0/C to 425/sup 0/C. The amount of conversion of kerogen to bitumen, oil, gas and residue products was obtained for different reaction times in this temperature range. Elemental analyses were obtained on the bitumen, oil, and solid reaction products. Molecular weights and /sup 13/C NMR measurements of the aliphatic and aromatic carbon fractions in the solid products were made to complete the analyses. The results show that the thermal decomposition of the New Albany oil shale exhibits complex behavior. None of the data fit a simple first-order kinetic expression with respect to kerogen concentration for all temperatures, indicating that multiple parallel reactions occur during the decomposition. However, by fitting the initial slopes of the oil conversion data, it was possible to obtain the weighted average rate constants at each temperature. These data gave a good fit to the Arrhenius equation with the frequency factor equal to 6.38 x 10/sup 15/ min/sup -1/, and the activation energy equal to 207.5 k.j mol/sup -1/ for the kerogen decomposition. The maximum bitumen concentration was 10% or less of the original kerogen at any temperature, indicating that direct conversion of kerogen to oil, gas and residue occurs during heating. Since the highly aliphatic Green River oil shale forms large amounts of bitumen whereas the more aromatic New Albany shale forms only small amounts, the formation of bitumen may be related to the aromatic nature of the kerogen. In general, the chemical properties of the oil were fairly constant at all reaction times and temperatures studied. Hydrogen sulfide was the dominant species in the gas phase. The solid and liquid nuclear magnetic resonance (NMR) data show that the net increase of total aromatic carbon in the products was about 30% of the raw shale value. 37 refs., 14 figs., 4 tabs.