Spin-lattice and spin-spin relaxation times and the ratios of local concentrations of paramagnetic species to their average values were determined for five petroleum bitumens differing in composition. It was found that the relaxation characteristics correlate with the bitumen composition. This correlation could not be revealed on the basis of conventional electron paramagnetic resonance (EPR) spectroscopy measurements. Hence, the determination of relaxation properties of paramagnetic species can be a useful supplement to the conventional EPR spectroscopy in studying petroleum bitumens.