This study is devoted to improving the heating to oil shale particles and in turn the yield and quality of shale oil in fixed bed reactors indirectly heated through use of internals. Metallic heating plates were vertically welded on the reactor wall as heating enhancement internals to provide extra heating surfaces inside the oil shale bed and to increase the high-temperature heating surface area by 35% to 210%. Comparison of heating rate to particles and shale oil yield was made between the reactors without and with the plate internals. Utilizing internals evidently enhanced the heating to oil shale particles and shortened pyrolysis time by 30% to 50%. The shale oil yield increased by 7% to reach 90% of the Fischer Assay oil yield (8.98 wt.%, dry base) when the heating surface area was increased by 70-110%. With increased heating surface area above 110%, the shale oil yield manifested conversely a slight decrease. Nonetheless, the fraction of light oil (boiling point <350 degrees C by analysis in simulation GC) was increased to about 66 wt.% from 60.94 wt.% for the reactor without any heating plate. Characterizing the char samples at different lateral positions of the oil shale bed justified that the flow of gaseous pyrolysis product in the reactor was guided to the vicinity of heat transfer plates to speed up gas exhaust and selective cracking. Consequently, adding heat transfer plates into an indirectly heated reactor would obviously intensify the heating to the oil shale bed and also elevate the pyrolysis oil yield and quality. (C) 2015 Elsevier Ltd. All rights reserved.