Abstract: The conditions of source rocks, reservoir rocks, and cap rocks are favorable in the southern segment of western sag of Liaohe Oilfield, where several favorable reservoir-cap rock associations come into being. The configuration of hydrocarbon generation and expulsion stage of source rocks and trap formation stage is reasonable in this region, which is favorable for forming lithologic stratigraphic oil and gas reservoirs with multi strata. Subtle oilgas reservoir types, such as stratigraphic, lithologic, and complex reservoirs, mainly developed in the region. Vertically, the distribution of subtle reservoirs is controlled by some main reservoir-cap rock combinations. Horizontally, controlled by the geological structure of sags, subtle reservoirs of various types developed in different formations. It is believed that favorable zones for the development of reservoir under the same sedimentary fractured zones, that is, transitional zones of slopes and depressions with abrupt or gentle slope, are favorable for developing lithologic oil and gas reservoirs

Key words: western sag of Liaohe Oilfield, combination of reservoir and cap rocks, subtle oil-gas reservoir, distribution regularity, geologic structure