Energy loss by fission fragments in nitrogen gas was studied by means of a pulse technique that measured luminescence excited by a low-intensity Cf252 spontaneous fission source. A novel kinetic analysis of competing emission and quenching reactions was developed that gives the power law dependency of energy loss by the fragments in a luminescing gas from the pressure at which maximum luminosity is observed. For nitrogen, the relationship E = E0(1−f)1.70 ± 0.07 is valid for 0.4 E0 < E < E0. The term E is used for the kinetic energy of a fission fragment of initial energy E0 that has traveled a fraction f of its total range.