A number of pour-point depressants of the ester and polyaminoaldehyde types have been synthesized. Their physicochemical and dielectric properties have been examined; by comparing these properties, additional information has been obtained to confirm the previously proposed mechanism of action of these additives and compositions thereof on solid petroleum hydrocarbons and the relation of the performance to the dielectric properties of the polyaminoaldehyde additives has been revealed, findings that can facilitate their selection in the development of inhibitors of asphaltene-resin-wax deposition in crude oil.