A process for producing mineral oil from mineral oil deposits, in which the mineral oil yield is increased by blocking highly permeable regions of the mineral oil formation by separate injection of at least one acidic formulation which comprises water-soluble Al(III) salts, and one urea- or urea derivative-comprising formulation into the deposit, said formulations not mixing with one another until within the deposit, and the mixture forming highly viscous gels under the influence of the deposit temperature. The process can be used especially in the final stage of deposit development, when watering out in production increases, and particularly after the steam flooding of the deposits.