On the basis of optical microscopy investigations of the behaviour of copolymers of higher alkylmethacrylates with vinyl acetate in diesel fuels of different fractional composition, and also experimental data obtained in an investigation of the depressive action of these copolymers, it is suggested that the mechanism of the depressive action of additives based on copolymers of alkylmethacrylates with vinyl acetate is based on associative interactions in solution between the n-paraffins of the fuel and the copolymers, for which, as for comb-shaped polymers, a proneness to the formation of associates, clusters and complexes with charge transfer is particularly characteristic.