The pyrolysis behavior of EL-Lajjun and Sultani oil shales was investigated under rapid heating conditions using a bench scale fluidized bed reactor. Shale particles were fed continuously (7 g h(-1)) in a bed of sand fluidized by N-2 gas. Experiments were conducted over a range of temperatures, 400-500 degrees C, and with three particle size fractions, 250-355, 355-500 and 500-710 mu m. Increasing the pyrolysis temperature resulted in increasing the oil yields, but at temperature over 475 degrees C, the increase became small. Over the tested range, particle size showed little effect on oil yields. A simple first order devolatilization model adequately describes the pyrolysis process. The rate constants and activation energies for the two shales were deduced.