Asymmetric aromatic polyimide membranes for a petroleum refinery were made by casting solution of 18 wt.% polyamic acid blending of the trade name Pyle-ML5057 (Du Pont Co.) and PMDA-DABP in the ratio of 1:1 and 20 wt.% phenanthrene in dimethylacetamide at 303-363 K, with 1 and 3-min evaporation times, followed by a cycle process of thermal treatment in a bath of dioctyl sebacate under N-2 in three steps : 1 h at 373 K, 1 h at 473 K and 1 h at 573 K. The asymmetric aromatic polyimide membranes fabricated with combinations of preparation conditions had a molecular weight (MW) cut-off ranging from 170 to 400 Da. The membrane which has a MW cut-off of 170 Da succeeded in separating the gasoline-kerosine mixtures. A separation factor (for gasoline/kerosene) of 19.5 was obtained.