The organic matter in oil shale is composed mostly of kerogen (insoluble in common organic solvents) with a few percent soluble bitumen. When Green River oil shale is heated to 573K, natural bitumen can be removed thermally from oil shale. The chromatogram of thermally separated bitumen is identical to that of the solvent-extracted bitumen (1). At temperatures above 573K, the kerogen decomposes to bitumen and subsequently bitumen to oil and gas (2,3). While considerable work has been done using Electron Paramagnetic Resonance (EPR) on coal (4,5) and western oil shale (6,7), relatively little is known about eastern shales. EPR measurements yield direct, in situ information on the kinetics of the organic-free radicals present in heated shale and natural bitumen. The present work was undertaken as a correlated EPR and TGA investigation of eastern shales to elucidate the pyrolysis mechanisms of these shales.