World-wide experience of retorting large particle oil shale demonstrates that known types of retorts are characterized by differing degrees of process efficiency. The latter depends on several factors influencing the process. In this paper an attempt in made to systematize the influence of these factors affecting, above all, the oil yield in vertical retorts. The present review, of course, does not pretend to be complete and does not consider all possible features playing a role in the process of retorting large particle shale under industrial and pilot-scale conditions. However, estimating the effect of those factors may be useful for further improvement of oil shale processing units. The comparison of data characterizing the efficiency of thermal processing of large particle oil shale in different types of retorts usually leads to the conclusion that the design features play a decisive role in efficient operation of the retorts. It is not sufficient, however, to consider the design features only. A great deal also depends on the properties of feed shale and the operating conditions in the process.