Laser magnetic resonance of the ${\mathrm{O}}_2$ molecule is observed using the 119- and 78-μm lines of the ${\mathrm{H}}_2$ O laser. The relevant transitions for the 119-μm line are $(N=13, J=14, M)\to (N=15, J=14, M^{\prime })$, and those for the 78-μm line are $(N=21, J=22, M)\to (N=23, J=22, M^{\prime })$, where $M^{\prime }=M or M\pm 1$ depending on the polarization. It is found that $g_{\perp }=2.0044\mathrm{}\pm 0.0008$, $g_z=2.0020\mathrm{}\pm 0.0001$, $g_n=0.000125\mathrm{}\pm 0.000008$ give slightly better agreement between theory and experiment than Hendrie and Kusch's values ($g_{\perp }=2.005169\mathrm{}$, $g_z=2.001939\mathrm{}$, $g_n=0.000122\mathrm{}$) and Bauer, Kamper, and Lustig's values ($g_{\perp }=2.004838\mathrm{}$, $g_z=2.002025\mathrm{}$, $g_n=0.000126\mathrm{}$), but the present experimental accuracy is not high enough to exclude these older $g$-factor values. Using the existing microwave data and the known laser frequencies, the zero-field frequencies for the transitions $\mathrm{}(N=J=13\mathrm{})\mathrm{}\to \mathrm{}(N=J=15\mathrm{})\mathrm{}$ and $\mathrm{}(N=J=21\mathrm{})\mathrm{}\to \mathrm{}(N=J=23\mathrm{})\mathrm{}$ are found to be 2496.283±0.30 and 3865.81±0.03 GHz, respectively. Combining these results with the frequency of the $\mathrm{}(N=J=1\mathrm{})\mathrm{}\to \mathrm{}(N=J=3\mathrm{})\mathrm{}$ transition obtained by McKnight and Gordy, we obtain $B_0=43.100518\mathrm{}\pm 0.000020$ GHz, $B_1=-0.14496\mathrm{}\pm 0.00030$ MHz, and $B_2=-0.17\mathrm{}\pm 1.00$ Hz.

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