In conventional reservoir simulation, wells are assumed to be at cell centers. Thus, the fluid flow pattern around an off-center well is represented incorrectly. This is especially true for large fieldwide models, which are gridded by very coarse blocks resulting in numerous off-center wells. This paper describes a new, rigorous method to model single or multiple off-center wells in a gridblock. Fluids can be drawn directly from the four closest neighboring cells into an off-center producer. Well location is honored exactly. With the new method, the calculated wellblock pressure can be interpreted at cell center rather than away from cell center as in the conventional approach. The new method is formulated fully implicitly, and although it adds more nonzero elements to the Jacobian matrix, its dimension remains unchanged. Therefore, implementation of this method is not difficult and the increase in computing costs is minimal. This work has been validated by fine-grid simulation results. Several single- and multiple-phase test cases are presented. We show that the new method can improve the accuracy of numerical results for large fieldwide models.