The condensates are generally characterized by high maturity, low concentration of steranes and terpanes biomarkers and low content of non-hydrocarbon fraction. In this case commonly used steranes, terpanes and carbazoles parameters cannot be effectively applied in the reservoir-filling tracing. The hydrogen bond formed by sulfur atom in the dibenzothiophenes (DBTs) results in molecule adsorption and fractionation during oil migration in reservoir. Like carbazoles, total DBTs content decreases with the increasing of oil migration distance. Therefore, a new parameter--total DBTs content is proposed to be used to trace the oil migration orientation and filling pathway. In present study, total DBTs contents of condensates and light oils are obtained by adding internal standard--eight deuterium atoms substituted DBT during Gas Chromatography-Mass Spectrometry analysis of aromatic fraction. Except for a few samples with much lower content of non-hydrocarbon fraction, the total DBTs content shows a fine positive correlation with that of carbazoles. Large errors can be caused in the process of pyrrolic nitrogen compounds separation. The application of this new parameter in the Fushan Depression of Beibu Gulf Basin, South China Sea indicates that this parameter is a reliable one to trace filling pathway in condensate reservoirs. Combined with other DBTs-related parameters, such as 4-/1-methydibenzothiophene and 2,4-/1,4-dimethyldibenzothiophene, oil migration orientation and filling pathway of the Fushan Depression was determined. The accumulations of Huachang oil field in the Fushan Depression are mainly migrated and charged from northeast to southeast along the Huachang uplift. It can be predicated that the light oil and condensates in the Huachang oil field should be sourced from the source kitchen at the Bailian Sag. It shows that total DBTs content is an effective parameter to tracing oil migration orientation and filling pathway. dibenzothiophene, alkyl dibenzothiophene, condensate reservoir, filling pathway, molecular markers, the Fushan Depression England et al. [1,2] first established a filling model of petroleum in sandstone reservoir, providing a scientific theory basis for reconstruction of oil migration pathways and orientation, definition of filling point and potential source kitchen as well as predication of "satellite reservoir" based on the differences of oil maturity, the oil/gas ratio, oil physical properties, etc. Since then, the focus of the petroleum geochemists has moved from exploration and increasingly towards production and reservoirrelated problems.Reservoir geochemistry has been developed and successfully applied in the petroleum exploration, reservoir appraisal and production monitoring [2] , but some limitations have been met in condensate and light oil reser-
