A controlled-gelation aqueous solution is proposed. The solution contains a hydrophobically-aggregating gelling agent, and an effective amount of an inhibitor which suppresses hydrophobic aggregation of the gelling agent. The inhibitor is soluble in water so that when the controlled-gelation aqueous solution contacts aqueous media the inhibitor disperses and gelation occurs. However, the inhibitor is substantially insoluble in hydrocarbons so that when the controlled-gelation aqueous solution contacts hydrocarbon media the inhibitor continues to suppress said hydrophobic aggregation and gelation is suppressed. The solution may be used to control the flow of water into oil wells, making it possible to reduce the water cut.