Diamondoid hydrocarbons have been identified in oil and source rock samples from the Tarim, Yinggehai, Qiongdongnan and other Chinese basins. Two diamondoid hydrocarbon ratios have been used as novel high-maturity indices to evaluate the maturation and evolution of crude oils and condensates in these Chinese basins. The two ratios, 1-MA/(1-MA + 2-MA) (%) (MAI = methyl adamantane index) and 4-MD/(1-MD + 3-MD + 4-MD) (%) (MDI = methyl diamantane index) were found to increase with increasing vitrinite reflectance. The initial values for the ratios are ca. 50 and 30%, respectively. Diamondoid hydrocarbons are products of rearrangement of polycyclic hydrocarbons and their ratios are found to be affected by organic input to a minor extent. Based on this study, crude oils from the Tarim Basin are generally believed to be very mature (R o > 1.1%). The Cambrian-Ordovician source beds are the major source rocks of crude oils and natural gases in this basin. Condensates from the Tarim, Yinggehai and Qiongdongnan Basins have higher maturities, equivalent to R o values of 1.6-2.0%. Gases and condensates from the Yinggehai and Qiongdongnan basins are generated mainly from Tertiary source rocks below 4000-5000 m.