There are potentially billions of cubic meters of liquid hydrocarbon available from oil shale of the Piceance Creek basin of western Colorado. This region is amenable to exploitation by a concept known as Vertical Modified In Situ (VMIS) combustion retorting. Field tests have been conducted with initial void volumes ranged from 20 -40%. However, low void rubbling technology has met with only limited sources in the field. The low void retort is designed to test different retorting parameters for rubble and fracture conditions in the range of 8-18% void volume.