1�� College of ��esources and Environment��Yangtze University��Wuhan 430100��China; 2�� Key Laboratory of Oil and Gas ��esources and Exploration Technology��Yangtze University��Wuhan 430100��China

To figure out the origin and sources of crude oils from Baiyun sag of the Pearl ��iver Mouth Basin�� the authors analyzed the distributions and compositions of various biomarkers in two kinds of crude oils from differ- ent tectonic units in the Pearl ��iver Mouth Basin systematically�� It is found that the Pr/Ph ratios of the crude oils from the north structures of the Panyu low uplift and panyu 4 sub-sag are relatively low ( ��2. 0)��which indicates that the terrigenous organic matter input is moderate��and the bicadinanes derived from dammar resin are almost ab- sent��the contents of rearranged steranes and hopanes are low�� However��C ₃₀ 4-methyl steranes related to dinoflagel- lates are abnormally abundant��and the ratio of C ₃₀ 4-methyl steranes and C ₂₉ regular sterane is more than 2.1��and the C _{19 ��26} tricyclic terpanes show a normal distribution while the dominant peak is C ₂₁ ��suggesting that algae has made an important contribution to original hydrocarbon parent material��which is consistent with that of lacustrine source rocks of the Wenchang Formation�� The Pr/Ph ratios of the condensates from the south structures of the Pan- yu low uplift and Baiyun sag are more than 4. 0��with abundant oleanane and bicadinanes��the contents of rear- ranged steranes and hopanes are relatively high��lacking C 30 4-methyl steranes�� While tricyclic terpane C _{19 ��26} presents the characteristics of the trapezium in turn reduce��indicating that terrigenous organic matter is their original parent material��which accords with the petroleum geology background of the development of coal-containing source rocks of the Enping Formation in the Baiyun sag��