Abstract: A releasable mounting apparatus for securely retaining of a cylindrical tank in an inverted vertical position adjacent to a seat back assembly of an emergency vehicle including a foot plate and a top clamping assembly between which a tank receiving zone is defined for receiving and holding of a cylindrical tank in the inverted position. The top clamping assembly can include a three part positioning apparatus including a rear positioning device and an upper centering guide as well as a top clamping member. Preferably the top clamping member is movable between a lower clamping position and an upper retaining position for facilitating securing and releasing of a cylindrical tank relative to the receiving zone thereof.