Four different approaches, including special core analysis (SCAL), log-inject-log, thermal-decay-time (TDT) logs, and material balance, were used to narrow the range of residual oil saturation (ROS) after waterflood, S(orw), in a carbonate reservoir in Qatar to between 23% and 27%. An equation was developed that relates S(orw) with connate-water saturation, S(wi), and porosity.