A system and process to deplete or remove oxygen in the ullage of a fuel tank to reduce the oxygen/fuel vapor ratio below a lower explosion limit by exposing the ullage compounds to an oxygen removal catalyst active at a relatively low temperature. The oxygen removal catalyst may be a non-precious metal catalyst. A selective reaction of the oxygen by the catalyst forms primarily alcohols, aldehydes, and/or ketones and produces less than about 5% water by volume. The selective reaction, occurring at the relatively low temperature, reduces the risk of flammability of the fuel.