Abstract: The 36-A Oil Field in Suizhong, Liaoning is a hundred million ton-sized oil-gas field in the Bohai offshore field. The Palaeogene oil reservoirs are mainly concentrated in the second member of the Dongying Formation. The present paper deals in detail with the microscopic features and controls of the hydrocarbon reservoirs in the study area. The favourable reservoirs are mainly organized in the lacustrine delta front subfacies in the second member of the Dongying Formation. The diagenesis, clay mineral content, temperature-pressure field and fluid filling as main controlling factors of the physical properties of the oil reservoirs are believed to be responsible for the devolopment of vast extensive distribution, tremendous vertical thickness, high porosity and high permeability favourable reservoirs.