Ammonia (NH/sub 3/) evolution during pyrolysis of three Green River Formation shales and one Eastern (Devonian) shale was studied. Most of the NH/sub 3/ that evolved during Fischer Assay-type pyrolysis was dissolved in retort water; the remaining NH/sub 3/ was trapped in an acid solution. Ammonia concentrations were measured with an NH/sub 3/-sensing electrode. We varied the peak pyrolysis temperature (PT) from 350 to 750/sup 0/C and the heating rate from 1 to 50/sup 0/C/min. The NH/sub 3/ yields increased rapidly above the oil-generating temperatures to a maximum at PT approx. = 700/sup 0/C and then decreased at PT = 700/sup 0/C because of decomposition of NH/sub 3/. The NH/sub 3/ yield showed no dependence on the heating rate at PT < 550/sup 0/C and decreased with increasing heating rate at higher peak temperatures. The maximum yield of NH/sub 3/ at PT < 500/sup 0/C reflected the organic nitrogen content. We developed a kinetic model for NH/sub 3/ evolution which takes into account the NH/sub 3/ generation from organic and inorganic nitrogen sources and NH/sub 3/ decomposition. 6 refs., 7 figs., 3 tabs.