A method and apparatus for an optical fuel detection system. The optical fuel detection system comprises an outer tube, and inner tube, and a set of optical fibers. The outer tube has a reflective inner surface capable of reflecting light and is configured to allow a liquid fuel to enter an interior of the outer tube on which the reflective inner surface is located. The inner tube is located within the outer tube in which an area is present between the reflective inner surface. The set of optical fibers are mounted to an outer surface of the inner tube. Each optical fiber has a core that is exposed on each part of an optical fiber opposite to the reflective inner surface and the optical fiber has a refractive index that is lower that the liquid fuel but higher than a gaseous form of any gas that may enter the area.