There is some evidence that in situ retorted shale oils may have generally lower heteroatom and polar compound concentrations than aboveground retorted oils. This could make in situ oils more attractive as an refinery feedstock or as fuel sources than aboveground produced oils. To help determine if differences in heterocompound composition might exist between oils produced in these different ways, light distillate fractions (400 to 600 F nominal boiling range) from two different types of internal combustion retorting processes, on aboveground and one in situ, were compared in analyses. Both oils were produced in forward-burn type processes in which the exiting oil had the opportunity for contacting raw oil shale or included minerals. The main difference in the two retorting processes was the time-temperature history of the oils produced. The aboveground process using crushed shale was a rapid-heat, high temperature process whereas the in situ process was apparently a slow-heat, low temperature process. Direct gas-to- solids heat exchange occurs in both processes. Other imponderables such as the contact of the product oil with raw shale or air in either case, or raw or spent shale in situ could, of course, affect the character of the oil also.