Comb-type poly(maleic alkylamide-co-alpha-octadecene) copolymers (MACs) with various ratios of polar carboxyl group/nonpolar octadecyl group were synthesized. Upon cooling, MACs change the size and shape of paraffin crystals, and reduce the pour point and yield stress of waxy oils, as observed by rheology, polarizing light microscopy, differential scanning calorimetry, and X-ray diffraction. They also reduce the paraffin crystallization temperature and enthalpies, inhibit the formation of layer structure of paraffin crystals. Their efficiency to improve the cold flowability was found to correlate to the ratio of polar/nonpolar group (r). MAC with r of 0.4, is more effective than the other two in improving the flowability of waxy oils. It seems that MAC2 can balance the competitive assembly behaviors of copolymers with paraffins and asphaltenes. The assembly between the carboxyl and amide groups of MACs with polar aromatic asphaltenes appears to stabilize crude oil by the steric effects of the long-chain alkyl branches of MAC polymers, thereby improving the flowability of paraffin/asphaltene gels formed upon cooling. (C) 2012 Elsevier Ltd. All rights reserved.