Liquid-level-measuring systems based on fiber-optics are under development as compact, lightweight alternatives to systems based on float gauges and other conventional sensors. For liquids that pose explosion hazards, fiber-optic sensors are inherently safer because they do not include electrical connections inside tanks. Fiber-optic sensors can be designed in many different forms to exploit reflection and transmission of light to measure liquid levels. Most of them are based on the effects of the indices of refraction of liquids on the waveguide properties of optical fibers: In a typical case, there is a loss of internal reflection of guided electromagnetic modes as a result of contact between the outer surface of optical fiber and a liquid. Hence, a substantial decrease in the light transmitted from one end of the fiber to the other is taken to indicate that liquid has come into contact with a suitably designed probe at the end of the fiber. A system capable of determining the level of liquid to within a known increment of depth could be constructed by placing the probes of a number of such sensors at known increments of depth in a tank.