Owing to industrial applications, a fiber optic displacement sensor is introduced to determine the concentration of hydrocarbons in water. Hydrocarbon is organic water pollution. It can harm the environment as well as human being. Thus, a reflective configuration technique was developed to study the hydrocarbon concentrations in the range of 0-20%. To validate the designed system, two concentrations were selected which represent the lower and higher region. In principle, this sensor is using the concept of intensity modulation as a function of displacement. The optimum displacement between the reflecting target and the fiber optic probe was found to be at 1.5 mm for all concentrations. Furthermore, the peak voltage from each fingerprint was found to be inversely proportional to the tested concentration. This implies that the higher concentration of hydrocarbon tends to detect weaker signal. The sensitivity of the fiber optic displacement sensor was found to be 0.12 mV/wt. % with repeatability of 96 %. The resolution of the sensor was 0.027 V, with a limit of detection of 0.23%. The linearity index was found to be 0.98 and 1.04 corresponding to 6% and 14% hydrocarbon concentration respectively. The simplicity and the credibility of such system offer a good opportunity for industrial applications especially in the environmental sector 1530-437X (c)