Abstract: A process and apparatus for determining the levels in a vessel of two or more immiscible or partially-miscible components has been developed. The process begins with transmitting gamma rays, x-rays, microwaves, ultrasound waves, or sonar waves through the vessel by sequentially activating at least three stationary energy sources positioned adjacent to and in the vertical plane of the vessel. A set of intensities of the energy exiting the vessel corresponding to each energy source is measured using an array of stationary sensors where each set contains the intensity sensed by each sensor in the array of sensors. The sensors of the array are positioned in the vertical plane of the vessel and in alignment with the energy penetrating the vessel. The array of sensors contains a number of sensors that is at least one greater than the number of energy sources.