Residual oil saturation (ROS), a key factor in the planning of tertiary recovery projects, can be determined on the basis of reservoir engineering concepts, core data, single-well tracer tests, and specialized geophysical well-logging techniques. Uncertainty limits of conventional logging techniques are not too promising. However, several log-inject-log techniques using multiple repeat logging runs will determine residual oil saturation within the range of ROS ± (≤ 5 saturation percent). Engineered planning of both logging and injection procedures is a prerequisite for reliable log-derived ROS estimates.