Abstract: Jiergalangtu sag is oil riched in Erlian Basin, where heavy oil reservoir, conventional oil reservoir and structural-lithologic reservoir were discovered one after another after three rounds of exploration. It features in coexistence of structural and lithologic reservoirs, and group distribution of heavy oil reservoirs and conventional thin oil reservoirs. There are various oil reservoirs in Jiergalangtu sag where hydrocarbon accumulation is complex. Continuous exploration is realized in oil enriched depression through changing thoughts in many aspects, such as structural to lithologic reservoir, slope to trough, shallow layer to deep exploration, etc. It is pointed out that new and big discoveries should only be realized by changing the way of thinking and deepening understanding continuously. There are still 50 million tons of remaining resources to be explored in the sag. Through illustrating known reservoirs and analyzing hydrocarbon occurrence rules, it is thought that the important direction of expanded structural reservoir is the two fl anks in slope belt of Baorao structure. There is greater potential in exploration of lithologic deposit in trough area. Tight reservoirs are important succeeding f ield for discovering large-scale reserves