A semiquantitative gas chromatography-mass spectrometric method relative to internal standard was developed for the fingerprinting analysis of bicyclic sesquiterpanes in crude oils.Based on the chromatograms properties,characteristic fragment ions(m/z 123,179,193 and 207) and the calculated retention indices,10 bicyclic sesquiterpanes compounds were identified and the concentration formulas of semiquantitation using the internal standard(d18-decahydronaphthalene) were provided.Bicyclic sesquiterpanes fingerprinting of 9 crude oils collected from Weizhou island，Bohai sea and crude oil from import sources were analyzed.The result revealed the following situation that the total concentrations of bicyclic sesquiterpanes range from 600 μg/g to 8 000 μg/g.The dominating components in all the studied crude oils are C15-sesquiterpane(BS3),C15-sesquiterpane(BS4),C16sesquiterpane(BS8) and 8β(H)-homodrimane(BS10),which account for 60% of total contents of bicyclic sesquiterpanes.The abundances of bicyclic sesquiterpanes in different oils follow an increasing order as Weizhou island > Bohai sea > crude oil from imports G1，G2.The total bicyclic sesquiterpane contents of G3(crude oil of GIRASSOL) and B3(crude oils from Bohai sea) are similar but exhibit different distributions of bicyclic sesquiterpane signatures.Crude oils from different offshore oil platforms in the same block exhibit very similar bicyclic sesquiterpanes signatures;In contrast,oils from different sources have different signatures of both the concentrations and relative distribution patterns of bicyclic sesquiterpanes compounds.Fingerprinting analysis of bicyclic sesquiter-panes in crude oils by semiquantitative method can achieve the identification of different crude oils.