In eastern China there are more than 100 Mesozoic-Cenozoic continental depressions; some of these have areas ranging from several hundred square kilometers to 2,000 km² (772 mi²). Many oil fields have been discovered in these depressions.

From the geologic and exploration histories of the Qianjiang, Miyang, and Damintun depressions the writer has summarized five essential features in exploring small depressions.

(1) Because the distance of oil migration is less than 50 km (31 mi) in continental basins, exploration in small depressions should be guided by the idea that source beds control hydrocarbon distribution.

(2) Locate the deep part of the depression by gravimetric and magnetic prospecting with some seismic profiling and drill stratigraphic wells in the deeper part to evaluate the capacity of oil generation and to record other geologic and geophysical parameters.

(3) Drill wildcats not only on the anticlines but also on structural noses and monoclines, because nonanticlinal pools commonly predominate (about 70% or more of reserve) in small depressions.

(4) If a few wildcats are dry holes and no sand beds are encountered during the early stages of exploration, negative conclusions should not be made in a hurry. If a possible source bed exists, further exploration should be conducted even if the area of the depression is less than 1,000 km² (386 mi²).

(5) In mature small depressions, exploration should be directed mainly to finding various subtle traps in the same way as exploring in large depressions.

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