A mathematical model of the pyrolysis of an oil shale particle, represented as an equivalent sphere, has been developed. The quantities of oil, gas, and carbonaceous residue formed from the kerogen initially present in the shale can be determined as a function of time for any specified heating cycle. Thermal decomposition of kerogen is represented by a kinetic scheme of ten endothermic irreversible first-order reactions whose temperature dependencies are formulated as Arrhenius equations. The calculated fraction of kerogen converted to shale oil is determined by this kinetic scheme, and the development of this scheme is presented in some detail.