Three one-dimensional and one three-dimensional physical simulations of forward combustion with steam-oxygen injection were conducted using Asphalt Ridge tar sand. One-dimensional simulations had steam-oxygen ratios of 3.1:1, 4.3:1, and 6.0:1 at oxygen fluxes of 10.8 to 8.0 scfh/ft/sup 2/. The three-dimensional simulation had a steam-to-oxygen ratio of 3.0:1. Results from the one-dimensional simulations show a reduction in the fuel deposition and oxygen demand as the steam-to-oxygen ratio increases. In conjunction with reduction in fuel deposition is the increase in combustion front velocity and oil yield with increasing steam-to-oxygen ratio. These trends are assumed to be the result of improved displacement efficiency of the steam zone that precedes the pyrolysis and combustion zones in the forward combustion process and suppression of coking by the steam. The effect of combustion front channeling was demonstrated by the three-dimensional simulation. Channeling caused a decrease in process sweep efficiency and oil yield with increased fuel consumption. Product oils from all simulations were significantly improved in quality compared with the original bitumen. The product oils had significantly lower molecular weights, viscosities, and percentage of components boiling above 1000/sup 0/F (538/sup 0/C). 12 refs., 10 figs., 6 tabs.