In a drift-tube study, four simple formulas, based on a dynamic equilibrium analysis of two gaseous ion swarms, are proposed to determine simultaneously the forward and reverse reaction frequencies together with two drift velocities. The formulas are put to the test for (N-4(+),N-2(+))/N-2 system with two arrival time spectra (ATS) generated from the experimental data previously reported at E/N=150 Td (the ratio of electric field strength to gas number density : 1 Td=10(-17) V cm(2)). The percent differences between the data and the determined values are estimated to be 0.8%, -1.4%, 6.8%, and 4.9%, for the drift velocities of N-4(+) and N-2(+) ions and the forward and reverse reaction frequencies, respectively. For the same system, two experimental ATS obtained at 180 Td by McKnight et al., being supposedly in near equilibrium, are directly examined by this method.