Precise measurement of the water fraction in oil is of critical importance in the oil industry. Currently, cost-effective, reliable, and compact downhole measurement technologies capable of full-range three-phase measurements are not available. This article presents an ultra low power, low cost, wireless, and noncorrosive resonance sensor based on magnetoelastic technology that has been implemented by an amorphous ribbon and electromagnetic interrogation. The proposed technology enables distinguishing all three gas, water, and oil phases with amplitude changes of 75% and 99% and resonant frequency shifts of 0.46% and 3.88%, respectively, compared to the gas phase. The response of the sensor enables characterizing the water-cut range from 10% to 90%. The addition of a Teflon anticorrosion layer enables sensor deployment for extended periods of time in harsh environments.