The present invention relates to a process for dyeing keratin fibres in which a mixture is applied to the fibres, this mixture being obtained from: a dye composition comprising at least one oxidation dye precursor, and an oxidizing composition comprising at least one chemical oxidizing agent, at least one of the compositions being dispensed from a pressurized container, the mixture of the two compositions comprising at least one thickening polymer chosen from: associative polymer, anionic non-associative polymer chosen from anionic polymers bearing sugar units, anionic polymers not bearing sugar units chosen from crosslinked acrylic or methacrylic acid homopolymers or copolymers, crosslinked 2-acrylamido-2-methylpropanesulfonic acid homopolymers and crosslinked acrylamide copolymers thereof, ammonium acrylate homopolymers, or copolymers of ammonium acrylate and of acrylamide, alone or mixtures thereof, and mixtures thereof; and also to a device suitable for performing this process.