The mass spectral decompositions of cyclic and acyclic borates have been examined. Straight chain trialkyl borates fragment by C-0 cleavage reactions accompanied by transfer of one or two hydrogen atoms, whereas tri-(sec-alkyl) borates primarily undergo a-cleavage reactions. Both types of cleavage are observed in the fragmentation of cyclic borates. B-0 bonds are not broken in the formation of most major fragment ions. The fragmentations of borates are compared with those * m/e values for B-containing ions refer to the mass of ions incorporating the llB isotope.