A CNG fuel tank system is provided for mounting on the roof of a bus. The system includes a support frame mounted on the roof of the bus. The support frame includes at least one longitudinal frame wall extending generally parallel to the length of the bus. Each tank cylinder has associated therewith first and second saddles which are attached to one side of one of the frame walls. Each saddle has a base oriented vertically and engaging in the first frame wall. Each saddle includes an arcuate recess spacing sideways from this frame wall. Each tank cylinder is received in the arcuate recesses of the saddles associated therewith. Each saddle has associated therewith first and second strap assemblies which extend around the tank cylinder to secure the tank cylinder to the saddles and thus to the support frame. Preferably, a set of four parallel tanks are mounted in the fashion described on two parallel longitudinal frame walls. There is one tank hung in a cantilever mode off either side of each frame wall. A center support is provided between the two center tanks for supporting a tank cover. One of the inner tanks may be removed without removing any of the other tanks. This is accomplished due to the cantilever mode mounting of the tanks and due to the removeability of the center support.