Photoabsorption cross sections of CH3OH, CH3OD, CD3OH, and CD3OD are determined in the spectral region 165--220 nm using synchrotron radiation as a light source. Excitation of methanol isotopomers in this wavelength region breaks mainly the O--H or O--D bond to form H or D, respectively. Significantly smaller absorption cross sections near the threshold region are observed for CH3OD and CD3OD. These data are used to calculate corresponding photodissociation rates by the solar flux at 1 AU. The rates for CH3OD and CD3OD are only about 80% and 82% of those for CH3OH and CD3OH, respectively. The effective photo-induced isotopic enrichment factors (per mil) are estimated to be 199? for CH3OD, -35? for CD3OH, and 154? for CD3OD. Such large enrichment factors are expected to induce detectable H/D fractionation in comets or elsewhere if the photo-induced isotopic fractionation effect is important in controlling methanol chemistry.