Abstract: In recent years, the volume method is widely used to perform reserve evaluation on new wells and the wells in early development in offshore oil and gas fields. However, evaluation results are changeable of some thin layers controlled by single well because it is difficult to determine the well-spacing control radius. This paper took wells which have already been put into production in East China Sea Oilfield as examples, based on the production-oil pressure relation curves in recent three years, using oil pressure drop method, calculated the cumulative gas production under the current wellhead pressure condition. Then compared the results with the actual accumulated gas production. The results show for closed lithologic gas reservoirs, the oil pressure drop method is an effective supplement to volume method to improve the accuracy of reserve evaluation. The research results have reference significance for SEC reserve evaluation of new oil and gas wells.