Abstract: With sedimentary facies as the key and the general rules of oil and gas accumulation as the basis, the author presents his views on where to find subtle oil pools of low permeability in the Yanchang Series. The paper is divided into two parts: 1)For accumulation of oil and gas, stress is laid on sedimentary facies that explains the vertical combination of source-reservoir-cap rccks and the lateral distribution of areas favourable for origination and accumulaticn of hydrccarbons; on the different oil pools formed in different facies zcnes and the relationship of the horizon of oil and gas accumulation with the lithologic properties of sandbodies and of the trapping conditions with lithology and lithofacies. 2)As to where oil is to be found, particular emphasis is laid on the delta in the eastern part of the basin and the tubidity fan in its western part where, in the opinion of the author, oil of commercial value may be found.