Using comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC x GC/TOFMS), the adamantane, diamantane and triamantane hydrocarbons were well separated with other alkanes and aromatics and distinguished clearly in the crude oils. Over 100 substitutions of adamantane, diamantane and triamantane were recognized, much more than the numbers identified with gas chromatography/mass spectrometry (GC/MS). In addition, they were not co-eluted or interfered with normal and branched alkanes. The diamondoids were aligned in flying geese spread on GC x GC chromatograms, which is typically presented in polyaromatic hydrocarbons but rarely among alkanes. This reveals that diamondoids should have undergone specially formation approaches, differently from most saturates and aromatics in petroleum. (c) 2012 Elsevier Ltd. All rights reserved.