Combination of two or more oil-soluble, polymeric materials having long linear side chains can be used to improve the flow properties of hydrocarbon oils containing high boiling waxes, such as fuel oils containing residua and crude oils. Examples of these polymeric materials include: condensation polymers of dicarboxylic acid or anhydride, polyol and monocarboxylic acid; addition polymers of: unsaturated esters, or long chain alpha monoolefins, or copolymers of said olefins with said unsaturated ester; polystyrene acylated with long chain fatty acid; etc. The invention also includes a method for formulating said polymer combinations to achieve an optimum effect in oil subject to pour point reversion, by giving samples of the oil containing the individual polymers a series of thermal histories, measuring the pour point of each of said samples to determine Flow Point, i.e., the highest pour point that the oil exhibits, and then blending the polymers to achieve a minimum Flow Point.