A process for the selective controlled reduction of the relative water permeability in high permeability, oil-bearing formations, with negligible reduction of the permeability to oil. The process comprises, for sandstone reservoir rocks, a first layer of cationic polymer, followed by a brine spacer slug and a second polymer layer made up of a suspension of anionic polymer and an anionic or non-ionic microgel, optionally this configuration being repeated. As a result the thickness of the polymer layer is considerably increased, which permits the process to be used in high permeability formations. For limestone rocks the first layer is made up of anionic polymer, while the second layer involves a suspension of cationic polymer/cationic or non-ionic microgel. The polymers are all injected as aqueous suspensions in brine or seawater.