The proton affinity of trimethyl borate was determined to be 197 +/- 3 kcal mol-1 by bracketing in both directions in a Fourier-transform ion cyclotron resonance mass spectrometer. This value was used to calculate a heat of formation of -46.3 +/- 3.0 kcal mol-1 for CH3O(H)B(OCH3)2+. Collision-induced dissociation threshold energy measurements carried out in a flowing afterglow-triple quadrupole instrument yield an activation energy of 39.5 +/- 3.5 kcal mol-1 for the dissociation of CH3O(H)B(OCH3)2+ to CH3OH and (CH3O)2B+. This bond dissociation energy, together with the heat of formation of CH3O(H)B(OCH3)2+, was used to calculate a heat of formation of 41.4 +/- 4.6 kcal mol-1 for (CH3O)2B+.