Method of reducing the pour-point and improving the flowability of petroleum oil or a fraction thereof by adding thereto a flowability-improving quantity of at least one copolymer of (a) an acrylic acid ester, a methacrylic acid ester, or a mixture of an acrylic acid ester and a methacrylic acid ester, and (b) not more than 20% by weight, based on the weight of the copolymer, of acrylic acid, methacrylic acid, or a mixture of acrylic acid and methacrylic acid, and wherein said esters in component (a) are esters of a C.sub.16 or higher alcohol or an alcohol mixture wherein at least 75% by weight thereof is one or more alcohols containing at least 16 carbon atoms; and the compositions resulting therefrom.