A multiplexing method for a fibre optic refractive index sensor is presented that is potentially capable of simultaneous measurement from many sensor heads, each of which is a cleaved fibre end. Associated with each sensor head are two fibre couplers and an optical fibre Bragg grating having a unique Bragg wavelength. Experimental characterization of the sensor network through the use of liquids with different refractive indices showed excellent agreement with numerical analysis and a precision of 0.002 RIU and resolution of the order of 10−3 RIU.