Experiments were conducted in a controlled-state retort at the Laramie Energy Research Center to determine the effect of oil shale particle size on the boiling range distribution of shale oil and unretorted bitumen. This study also provided insight about the movement of shale oil over unretorted oil shale. Oil shale, in the particle size ranges 3/64 to 3/8 inches, 1/8 to 1/2 inches and 3/8 to 3/4 inches, was retorted in interrupted and completed experiments. All experiments were conducted with nitrogen as the carrier gas to avoid combustion. Data included the amounts of shale oil and unretorted bitumen recovered, boiling range distribution of the shale oils and bitumens, analyses of the shales, and effluent gas compositions. Analysis of the data showed that the smallest oil shale particles 1) retained more shale oil on their surface, 2) allowed shale oil to emerge from the oil shale at a lower temperature, 3) yielded a lower boiling crude shale oil, and 4) retained more carbon residue on the retorted shale.