SPE-PRMS is usually used to classify and categorize overseas lithologic reservoirs resources and reserves, but there exists no methods of classification, categorization and evaluation for lithologic reservoir reserves. In order to standardize the reserves evaluation of overseas lithologic reservoirs, based on definitions, uncertainty ranges, lithologic boundaries, oil (gas) water interfaces, tight layer blocking zones, etc., of P1, P2, and P3 reserves, this thesis propose a method for classifying and categorizing reserves of overseas lithologic reservoirs, and determining lithologic boundary, oil bearing area, and effective thickness. The research results indicate that ①reserves classified as P generally require a development plan approved by the company or the host government of the resources. For lithologic reservoirs, P1 reserves are calculated according to wells with commercial production or commercial test flow rates, the area of which is usually determined by the drainage area of the producing well (1.5 times the development well spacing) and the extent of the known gas bottom or known oil top and known oil bottom. Reserves within half the distance from the P1 reservoir boundary to the lithologic boundary are P2 reserves; Between the centerline and the lithological boundaries there are P3 reserves. If there is no oil–water (or gas–water) interface within the trap or it is not yet possible to be located, the P3 reserves shall be determined in accordance with the trap spill point. If the lithology or physical properties of the reservoir change dramatically, P2 reserves can be determined by extrapolating one development well spacing according to P1 reserves, and P3 reserves by extrapolating one development well spacing according to P2 reserves. ②If the distance from the P class reserve well to the pinch-out line of the permeable reservoir is not greater than 3–4 times the development well spacing, for medium–high porosity reservoirs, the pinch-out line can be directly regarded as the lithological boundary; for low porosity reservoirs, the lithological boundary is the effective thickness contour that is proven to achieve P class reserves. The oil- and gas-bearing area of lithologic hydrocarbon reservoirs is determined by a synthesis of lithological boundary, hydrocarbon-water boundary and tight layer blocking zone, etc., in which the wells should meet the standard of P class reserves. For hydrocarbon reservoirs with identified fluid interfaces, the fluid interface used to define the hydrocarbon-bearing area should be confirmed by drilling and coring data or test data, while for reservoirs where no fluid interface has been identified, the location of hydrocarbon-bearing area should be consonant with the lowest tested and confirmed bottom boundary of the oil and gas formation, or the extrapolated circle of the effective thickness value. ③The effective thickness of a P1 reservoir shall be supported by reliable stratum test data that demonstrates its productive capacity or by sufficient log data that demonstrates with a high degree of confidence that the evaluated formation segment makes a significant contribution to production. For determination of effective thickness of P2 reserves, there is devoid of conclusive test data, and there is not such an explicit sign on its log curves to prove the production capacity of the layer and segment evaluated as that of P1 reserves. The P3 reservoir has a greater degree of uncertainty in effective thickness, particularly with respect to its potential contribution to production, due to uncertainties in petrophysical interpretation. ④the volumetric method is recommended for lithologic hydrocarbon reserve assessment. To illustrate, the classification and categorization of reserves in lithological reservoir and reserve evaluation method, overseas oilfield A is taken as an example.