Abstract: By means of chromatography-mass spectrography and gas chromatography, isoprenoids (i15-i20) have been identified in 49 crude oil samples and 3 rock samples from oil fields in Shengli, Huabei, Subei, Dagang, Liaohe and Daqing and also from Sichuan, Gueizhou etc. The relative contents, in percentage, of phytane (Ph), pristane (Pr), norpristane (i18), 2. 6.10-trimethyl-tridecane (i16)and farnesane (i15) are determined, as well as the ratios of Pr/Ph, Pr/nC₁₇, Ph/nC₁₇ and (i18+i16+i15)/(Ph+Pr). The curves of the relative contents of Ph, Pr, i18, i16 and i15 may show the character of different oils, useful for correlation purpose. The evolution of isoprenoids in crude oils is divided into sub-mature stage (Pr/Ph>0.8, (i18+i16+i15)/(Ph+Pr)=0.2-0.5); mature stage (Pr/Ph>0.8, (i18+i16+i15)/(Ph+Pr)=0.3-0.6) and highly mature stage (Pr/Ph>1.0, (i18+i16+i15)/(Ph+Pr)>0.6).