With a recovery factor of ~51% and watercut in excess of 97%, the Minas Field in Sumatra Indonesia can certainly be categorized as mature field. Recently, the field has experienced a steep production decline, along with increased operating costs. As a result, a waterflood optimization study was initiated. This paper discusses the reservoir simulation to optimize the waterflood operations. The simulation, a sector model for sections 8C, 8D, and 8E, was used to test various prediction schemes such as pattern realignment and infill drilling. A seven well infill program is in progress to test for unswept oil.