Abstract: Most water-oil contacts of reservoirs are usually dipping, which is caused by the regular change of property of reservoir rock, and is not related to the current water-flow underground. Oil and gas pouring to reservoirs is also not the main cause of dipping of contacts, because the pouring rate is not high enough to dip the water-oil contact to certain content. The balancing of water-oil contacts takes quite short time, so the contacts of the most reservoirs are in equilibrium state at present, only a few reservoirs are still in adjusting.

Key words: reservoir, water-oil contact, oil/gas pouring, balance