The present paper proposes a model for the action of the oxidizing gases O-2 and NO2 on the electrical conductivity of polyfluoro-aluminum-phthalocyanine thin films. The proposed doping mechanism makes it possible to separate the physical process (physisorption, diffusion, displacement of previously adsorbed species) and the chemical process (chemisorption or charge transfer). Because of their different kinetics, these two processes are clearly seen in the transient response of the film conductivity which follows a sudden change in the temperature. Several experimental results obtained in our laboratory, or quoted in the literature, can be explained by our model, especially the power-law dependence of the conductivity on the gas concentration. Conclusions are drawn about the use of such films as sensitive elements for gas sensors.