We report an investigation of the ${\mathrm{b}}^{1}$${\mathrm{\ensuremath{\Sigma}}}_{\mathrm{g}}^{+}$(v=0)\ensuremath{\leftarrow}${\mathrm{X}}^{3}$${\mathrm{\ensuremath{\Sigma}}}_{\mathrm{g}}^{\mathrm{\ensuremath{-}}}$(v=0) band of $^{18}\mathrm{O}_{2}$. The weak magnetic-dipole transitions around 761 nm were observed using a high-sensitivity absorption spectroscopy apparatus based on a DFB diode laser source and a multipass absorption cell. We accurately measured the wavelength of several lines and deduced the rotational constants for the ${\mathrm{b}}^{1}$${\mathrm{\ensuremath{\Sigma}}}_{\mathrm{g}}^{+}$(v=0) electronic state. We also studied the line broadening in the presence of different isotopic species and determined the pressure broadening coefficients. We discuss the interest of these data in view of a possible test of the symmetrization postulate for $^{18}\mathrm{O}$ nuclei.