Demonstration of the use of radioactive tracers to monitor saturation distributions as a lower-cost alternative to computerized tomography scanning. In this method the injected fluids are labeled with radioactive tracers and the subsequent gamma radiation is monitored with a movable detector. This technique provides a 1D fluid-saturation profile along the length of the 2.5-ft core samples. Various experimental results, including a miscible displacement of inactive brine by radioactive brine, are presented. the saturation profiles provide the saturation front velocity and the development of local saturation variations as functions of time and position.