A novel, real-time, non-contact, non-invasive and high-sensitivity planar microwave sensor is developed for water cut measurements of crude oil samples. This sensor demonstrates the capability of measuring water cut of bitumen in real-time, which is of low-cost and eliminates the hurdles of current measurement techniques, prevents loss of production, and paves the way for oil field automation. The platform of the proposed sensor is based on a passive split ring resonator-based sensor with a defected ground gap coupled transmission line as the reader. The performance of the microwave sensor has been verified with varying water concentration in oil samples. The non-contact nature and high-resolution of the proposed structure enables monitoring of water cut in the full range.