Geometries of stacked oil shale bricks, with overall void volumes ranging from 12% to 15%, were combustion retorted in a batch, pilot scale sized retort. Experimental parameters were total void volume, richness of shale, particle size, and retorting gas flow rate and composition. A "base case" of experimental conditions was chosen to be in the region of commercial interest and the experimental parameters were varied one at a time from that base case. Oil yield was the dependent variable. Results indicate retorting of oil shale at very low voids is possible and efficient but pressure drops would be relatively high. Particle size change was the only parameter that affected oil yield significantly in the range of void volume investigation.