Abstract: Aer sag in Erlian Basin is one with reversal anticline structures, which is formed through multi-stage activities. Study of the hydrocarbon accumulation conditions of the sag shows that the main hydrocarbon source rocks are distributed in the K1ba and the upper section of K1bt1.Main oil layers include the upper section of K1bt1, the lower section of K1bt1, K1ba and Pz. Fan-delta is the main sedimentary type. Reservoir properties are generally poor, but high-quality reservoir develop in the poor reservoir, the best one is in the lower section of K1bt1. Four sets of reservoir developed in Aer sag. The main reservoir types include inverted anticline, broken nose, structural-lithologic reservoir, and tuff buried-hill reservoir in west-slope. Aer sag is another oil-rich sag in Erlian Basin

Key words: hydrocarbon accumulation condition, reservoir type, structural inversion, Aer sag