The present invention provides a narrow band infrared water cut meter for detecting a full water cut range of a flow stream. The water cut meter includes a light source probe for irradiating the flow stream with a narrow band of infrared light and a light detector probe for sensing infrared light passed through the flow stream. For a narrow band of infrared light of a predetermined wavelength, there is a large difference in the absorption of infrared radiation between oil and water. At such a wavelength, the narrow band of infrared light is substantially transmitted through water content and gas content of the flow stream and substantially absorbed by oil content of the flow stream. The water cut meter thus differentiates oil by treating gas like water. Unlike other water cut meters, the narrow band infrared water cut meter is independent of variations of oil and water densities, salinity, oil emulsions, varying flow rates, and the gas content of a flow stream.