For more than sixty years the rich oil shale formations of Colorado, Utah and Wyoming have been evaluated as a future source of petroleum. After many false starts, including the recent problems due to the economic conditions, the commercial production of shale oil will commence with the 1984 start-up of the Union Oil project near Parachute, Colorado. Other companies continue their interest and await only better economic conditions to become active again. This paper reviews some of the major elements involved in the production of shale oil with emphasis on means available to express the efficiency of production of pyrolysis liquids from oil shale rock.