Remaining oil saturation established by waterflooding from maximum initial oil saturation was measured in Indiana limestone under four mixed-wet conditions established using different organic acids. The altered wettability is characterized by the advancing contact angle of the aqueous phase on a calcite substrate submerged in the oil phase, which ranged from θo = 50° to 150°. Remaining oil saturation decayed as a power of time for up to 55 pore volumes of water injected and then reached a constant value. The duration of oil production increased linearly with θo. In contrast, remaining oil saturation decreased and then increased with increasing θo within the range of experimental conditions, with optimal wettability for recovery shifting from θo = 110° to 135° as waterflood progressed.