Abstract: In order to properly evaluate the oil and gas volumes in place,the reasons for volume uncertainty are demonstrated.The technical limitation,data limitation and subjectively parameters selection listed as the main causes of volume uncertainty.Uncertainty analysis based on 3 D geological modelling are studied due to the uncertainty in the input data and inconsistency between them.The volume uncertainty analysis workflow is established and the geological parameters affecting volumes are summarized as top surface,sand distribution,fluid contacts,porosity,water saturation and volume factor based on the study in an oilfield of Niger delta basin.By taking P reservoir of Niger delta basin in west Africa as an example,the system analysis of the geological reserves evaluation of oil and gas reservoirs of the uncertainty of the geological factors is carried out,which points out the top surface structure and sand body distribution,fluid interface,reservoir parameters are the main factors affecting geological reserves calculation results.Uncertainty analysis of oil and gas volumes in place by using 3 D geological modeling method properly indicates the risks in volume estimation,which provides the basis for scientific decision in investment,well placement and production planning.