In geophysical and geochemical oil-gas exploration, uncertainty would cause assessment of prospects to fall into trouble. The use of geophysical and geo chemical data would reduce but could not eliminate the uncertainty. The use of data in different stages of decision making would also help to promote exploration effectiveness and increase the ratio of success. Introduction of pro bability methods would improve the current interpretation status in explora tion and enable the assessment and decision making to be performed on the quantitative basis.