Abstract: There are three types of oil flow away in oilfields developed by water injection, i . e. (1) oil flow away in oil—water transition zone, (2) oil bypass into gas cap, and (3) oil bypass into shallow formation along wel I bore (in the wel Is with bad quality of cementing bonding ) or fault . Major factors leading to oil flow away are high pressure injection and unbalance of injection and production.The three types abovementioned exist in all oi 1 fields with various extent. Practice of Daqing oilfields development demonstrates that all the abovementioned three situations are present. In order to reduce loss of oil reserve resulted from oil flow away, it is neccessary to take certain technique in development and welldri11ing.