High-performance liquid chromatography (HPLC) followed by comprehensive two-dimensional gas chromatography (GCxGC) was used for detailed group-type characterization of hydrocarbons present in motor oils. With conventional CC, motor oil is not well separated due to its complexity, resulting in a "hump" in the chromatogram: the unresolved complex mixture (UCM). With HPLC-GCxGC, motor oil hydrocarbons can be quantitatively separated into four major groups: alkanes, cycloalkanes, alkenes and aromatics. Each group can be further separated and divided by ring number or carbon number. Three selected motor oil samples were characterized by HPLC-GCxGC including two conventional motor oils and a synthetic motor oil. Using a proprietary silver-modified HPLC column, the aromatic components in motor oils were baseline separated from the aliphatic UCM and were then further separated by GCxGC based on their aromatic ring numbers. Accordingly, the aliphatic components were separated by GCxGC based on their saturated ring numbers. This paper illustrates the capabilities of HPLC-GCxGC for reliable and detailed quantitative group-type characterization of hydrocarbons present in motor oils. (C) 2008 Elsevier Ltd. All rights reserved.