Abstract: 100 column samples have been collected from the middle Bohai Bay Basin in order to test the efficiency of the method of φ_iC4/φ_nC4 and φ_iC5/φ_nC5 in oil and gas exploration. The acidolysis hydrocarbon contents have been analyzed and tested. The content of nC₄ in each layer is generally higher than the content of iC₄, and the iC₅ content of each layer higher than the content of nC₅, and the iC₄ and nC₄ data integrity is much better than the iC₅ and nC₅ data integrity. We picked 11 typical sets of data out from the φ_iC4/φ_nC4 value center for study of the vertical changes and found that the heterogeneity plays a leading role in the differentiation, and dominates the migration path and direction of the light hydrocarbon. The contour map of φ_iC4/φ_nC4 corresponds well with the counter map of AC₄ in the study area where the φ_iC4/φ_nC4 value is greater than 0.85 as the background. The φ_iC4/φ_nC4 value is treated as anomaly if it is less than 0.85. We can find out the distribution pattern of oil and gas in the exploration area by study of the relationship between heterogeneities and lighter hydrocarbon anomalies. The standard of anomaly has important means to the hydrocarbon anomaly assessment in the Bohai Bay Basin.