In situ recovery technologies for tar sand deposits and heavy oil reservoirs are simulated at the Western Research Institute to develop a technological base for understanding the application of in situ processes to these resources. Wide ranges of process parameters are tested in a one-dimensional tubular reactor system. Three-dimensional process performance is evaluated by testing the most promising operating parameters, as determined in one-dimensional simulations, in consolidated blocks of the field resource. A three-dimensional simulation of forward combustion was conducted on a block of material from the Tar Sand Triangle deposit. Although combustion was established in the block, the maintenance and advancement of the combustion front was not successful. Problems relating to maintaining and advancing the combustion front were analyzed. To overcome these problems, it has been determined that: (1) larger heated area must be established prior to unheated air injection, and (2) continuous monitoring of oxygen in the produced gas must be used to control air injection rates. 2 refs., 5 figs.