"The ignition characteristics of oil shale beds using hot air have been investigated. The velocity and temperature of the air, and the particle size and grade of oil shale have been identified as the key parameters. The effects of these parameters on the time and energy required to attain a self-sustaining retorting front have been determined in this work. Gas-solid heat transfer, intraparticle thermal conduction, kerogen decomposition kinetics, or a combination of these control the ignition process. Depending on the conditions, the time required to attain self-sustained retorting ranged from 4.5 to 112 minutes. The energy input ranged from 0.17 to 7.97 kcal/cm2. The ignition time decreases with increasing flow rate and air temperature, increases with increasing size, and passes through a maximum with increasing shale grade. The energy input decreases with increasing air temperature and increases with increasing particle size. It passes through a minimum for increasing flow rate and a maximum for increasing shale grade"