Notes. Column 1 gives the serial number of each transition (for reference in the text). Columns 2–4 give the transition, rest frequency and short line name of each methanol transition, respectively. The frequencies of methanol transitions are adopted from Müller et al. (2004), marked by an asterisk, and references for the other methanol transitions are: ^α the CDMS database (Müller et al. 2005); ^β Coudert et al. (2015); ^γ Mehrotra et al. (1985). The frequency uncertainties are given in parentheses in units of the least significant figure. Column 5 shows the classification of methanol maser transitions. Column 6 gives the upper level energy of each transition. We note that the E-type ground state (1₋₁) level is at 7.9 K. Column 7 gives the critical density of each transition which is calculated by assuming optically thin transitions and a gas kinetic temperature of 100 K. The corresponding code is available from https://github.com/yxlinaqua/molecule_basic. Column 8 lists the reference for W31C: (1) Caswell et al. (1995a); (2) Breen et al. (2010); (3) Breen et al. (2014); (4) Haschick & Baan (1989); (5) Breen et al. (2019); (6) Slysh et al. (1999); (7) Wilson et al. (1985); (8) Menten et al. (1986a); (9) Menten (1991b); (10) Caswell et al. (1995b); (11) Caswell (2009); (12) Green et al. (2010); (13) Forster et al. (1990); (14) Kurtz et al. (2004); (15) Kim et al. (2019); (16) Chen et al. (2012); (17) Menten et al. (1986b); (18) Wilson et al. (1984). Column 9 gives the note for W31C, and the note for the corresponding transitions towards W3(OH) can be found here: (a) maser; (b) all observed J₂ − J₁E lines near 25 GHz are shown inverse P-Cygni profile; (c) absorption; (d) thermal emission.