An analytical method that provides chromatographic information regarding gas oil resins has been developed. This method uses a high performance liquid chromatographic system without backflushing and a single hyper-cross-linked polystyrene column. The use of the latter was warranted as it retains aromatic model compounds more effectively than a typically used silica-based amino-cyano column. Moreover, there was no need for extra solvent drying techniques because a retention time reproducibility of 2.9% RSD over 6 months was achieved. Using this method, gas oil resins were separated into seven chromatographic regions in 35 min on the hyper-cross-linked polystyrene column using a four-solvent-gradient procedure (hexane, chloroform, tetrahydrofuran, and methanol). On the basis of model compounds, separation was achieved between aromatics, sulfur-containing, and nitrogen-containing compounds. Determining composition has a large effect on the characteristics, conversion, and uses of the petroleum feedstock. As resins comprise a significant component of petroleum feedstock-up to 54% of the source material-the detailed characterization of resins using this method is expected to assist in improving the valorization of petroleum products.