A comparative study of the properties of poly(decyl methacrylate) and decyl methacrylate copolymers with N-tert-nonylacrylamide as viscosity index improver-dispersant additives for petroleum oils has been performed. Tests in the I-20A oil have shown that the introduction of substituted acrylamide units improves the thickening and dispersing properties of the poly(meth)acrylate additives, but it reduces their resistance to mechanical degradation.