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tokens: frequency of the observed maser transition. We use A = 5.570 × 10 −8 s −1 , the highest Einstein coefficient in Lankhaar et al. ( 2018 ) for the ν = 24959.079 × 10 6 Hz CH 3 OH maser transition, and T b = 10 6 –10 7 K, ΔΩ ≃ 0.03–0.003 for the 25 GHz maser line (Leurini et al. 2016 ). Using these values in Equation ( 2 ), we obtain R ≤ 3 ×10 −3 s −1 . Meanwhile, g Ω ≈ 170 s −1 in our observations of OMC-1. This means that R ≪ g Ω, and thus it is unlikely that a rotation of the axis of symmetry for the molecular quantum states is responsible for the shape of the Stokes V profile. Finally, Houde ( 2014 ) found that maser radiation scattering off foreground molecules can increase the antisymmetry in the Stokes V spectral profile of SiO masers. Consequently, if the Stokes V profile were ascribed to the Zeeman effect, one would obtain a much larger value for the magnetic field traced by these SiO masers. While we cannot rule out this effect in our 25 GHz CH 3 OH maser observations, our values are not orders of magnitude higher than the fields expected in such regions, unlike in SiO masers. We will discuss this in more detail in the next subsection. 4.3. Magnetic Fields and Densities If the observed Stokes V profile is caused by a magnetic field in the source, and is not due to any instrumental effects or other non-Zeeman causes discussed in Section 4.2 , then we have a magnetic field from our 25 GHz Class I CH 3 OH maser observation of OMC-1 that is three to four times larger (depending on which hyperfine is responsible for the maser) than the highest magnetic field we have detected to date in Class I CH 3 OH masers at 44 GHz (Momjian Sarma 2017 ). Such a value is not implausible, however; if we assume that the fields are amplified in proportion to the density in the shocked regions where these masers occur, thenwhere B pre and B post are the magnetic fields in the pre- and post-shock regions respectively, and n pre and n post are the densities in these regions. We can use Equation ( 3 ) to calculate B pre and compare it to magnetic fields calculated from other observations. Since our measured fields are in the range 171–214 mG depending on which hyperfine is responsible for the maser transition (Table 3 ), we will use = 171 mG in our calculations; this is convenient because values corresponding to = 214 mG can then be found by multiplying our results by a factor of 1.25. Leurini et al. ( 2016 ) have found that bright Class I methanol masers likely occur in regions with densities in the range 10 7–8 cm −3 , so we will calculate corresponding to both n post = 10 7 and 10 8 cm −3 . For densities in the pre-shocked gas we draw upon the work of Kwan et al. ( 1977 ), who found that a minimum pre-shock density of 10 5 cm −3 is required to produce the observed intensities in the H 2 ν = 1−0 emission lines in OMC-1. Thus, densities in the pre-shocked material of interest are likely of the order of 10 5 cm −3 or higher, but unlikely to be as high as, or