A one-dimensional model of condensed phase exothermic combustion with gas generation is developed. The numerical calculations show that the constant pattern propagation regime moves to higher values of the dimensionless heat of reaction gamma and the dimensionless activation energy, in comparison with gasless combustion. The propagation velocity increases due to the temperature overshoot. The effects caused by heat loss, variable thermal conductivity and temperature overshoot due to gas generation, are discussed. The changes introduced by gas generation deteriorate combustion stability. The model can be used to assist in design of so-called "oxygen generation devices".