these methods reduced the predilection of oxygen to enter the wellbore but gave surprising and counterintuitive benefits the oil recovery factor increased and build up of coke in the wellbore decreased consequently higher oxidizing gas injection rates could be used while maintaining safe operation it was found that both methods of adding steam to the reservoir provided advantages regarding the safety of the thai u2122 process by reducing the tendency of oxygen to enter the horizontal wellbore it also enabled higher oxidizing gas injection rates into the reservoir and higher oil recovery extensive computer simulation of the thai u2122 process was undertaken to evaluate the consequences of reducing the pressure in the horizontal wellbore by injecting steam or non oxidizing gas the software was the stars u2122 in situ combustion simulator provided by the computer modelling group calgary alberta canada table 1a shows the simulation results for an air injection rate of 65 000 m 3 day standard temperature and pressure into a vertical injector e in fig1 the case of zero steam injected at the base of the reservoir at point i in well j is not part of the present invention at 65 000 m 3 day air rate there is no oxygen entry into the horizontal wellbore even with no steam.