Abstract: The effectiveness of the oil and gas geochemical exploration indicators includes the stability of the geochemical field of the indicators,the efficiency of the indicators in reflecting the underground oil and gas,and the reproducibility of the geochemical anomalies.A follow-up study of the geochemical indicators over a subtle fault block oil reservoir in Linnan area,the Bohai Bay Basin,including acid-extraction hydrocarbon,headspace hydrocarbon and alteration carbonate,has been conducted.The results show that the geochemical indicators of the acid-extraction methane,the heavier acid-extraction hydrocarbons,and the alteration carbonate have stable geochemical field in the study area;whereas the geochemical fields of both the headspace methane and the heavier headspace hydrocarbons are less stable.The study also indicates that the acid-extraction methane and the alteration carbonate are the main effective geochemical indicators above the subtle fault block oil reservoir,while the headspace methane is the minor effective geochemical indicator.The special geological role of faults in the oil reservoir geolo-gical system and the effect of faults on the anomaly distribution regularity of the acid-extraction methane have been discussed,and the halo anomaly pattern of this geochemical indicator has been determined over the subtle fault block oil reservoir.