A flex fuel sensor is deployed in conjunction with the fuel transfer line (e.g. around a plastic fuel line) or at the bottom/side of a fuel tank. An RF signal of a constant frequency may be generated across a resonant circuit, which comprises of an inductor and a PCB trace capacitor, capacitor plates, semi cylindrical capacitor plates, or the like. Electromagnetic radiation is propagated into the passing fuel in the transfer pipe. The conductivity and dielectric properties of the fuel change the capacitance of the trace capacitor/capacitor plates. These changes are proportional to ethanol/alcohol content of the fuel and are preferably detected by a microcontroller, or the like, and then transmitted to a flex fuel vehicle Engine Management System.