Abstract: Saudi Arabia ranks number 1 in the world in terms of oil and gas resources. In geology, it could be divided into 5 stages of evolution. It started as a salt basin in the time of Precambrian, and then filled with clastic deposits in Paleozoic, shallow marine shelf sediments in Late Permian-Triassic, shelf basin deposits in Jurassic-Cretaceous and basinal deposits in Cenozoic, which gave birth to three major sets of reservoir combinations, including the Permian, Jurassic and Cretaceous reservoirs, and thus created favorable conditions for the accumulation of large amount of oil and gas. Deep Paleozoic reservoirs with low porosity and permeability in some matured fields as well as unconventional oil and gas will be the main targets for Chinese Petroleum Companies to look for in cooperation with Saudi Aramco in the upstream fields.