Abstract: Subtle oilgas pool has been the explorative emphases in Bohai bay basin and the lithologic pool is the important aim for reserves improvement. But the exploration in recent years indicated that the different petroliferous quality of lithologic trap is very distinct. The estimate that if the trap is oilbearing or not and how much is the fullness degree of lithologic trap has been indispensably important technology in the whole course of decisionmaking of exploration， arrangement of well position and exploitation of oil field. On the basis of geological statistics and AHP(analytic hierarchy process) analyses of 236 lithologic traps of Dongying depression， the main controlling factors of reservoir formation are found out and rationed. Then making use of multilinearity regress method， the fullness degree forecast models of lithologic trap at each structural zone in Dongying depression are established. The validation results of this forecast models indicate that 80% forecast fullness degree of lithologic trap is consistent to the factual value，implying that the forecast method can be used in oil and gas prospection.

Key words: Bohai bay basin, lithologic reservoir, petroliferous property, fullness degree, quantificational forecast