Abstract: The generalized water displacement curve formula derived from the classical one can correspond to many relations between cumulative oil production and water cut, reflect the different water cut trends in the waterdrive oilfields, describe and predict the changes in water cut and cumulative water-oil-ratio, and calculate the recoverble reserves, especially the ones in successive years. So it possesses higher theoretical and pratical values.

Key words: Water displacement, Displacement curve, Equation, Derivation, Water cut, Recoverable reserve, Recovery percent