Ab initio calculations at the MP2/6-311++G(3df.2pd) and CCSD(T)/cc-pVTZ levels were carried out to calculate the structure and energetics of isomers of singlet XH2+ (X = B, Al and Ga). Energy comparison shows that although the linear D-infinity h structure 1a is the global minimum for BH2+, the global minima of AlH2+ and GaH2+ are not of D-infinity h symmetry 2a and 3a. respectively, but of C-2v symmetry 2b and 3b with a 3c-2e bond. The D-infinity h symmetric 2a and 3a are significantly less stable than 2b and 3b, respectively, by 13.1 and 21.5 kcal/mol. Relative hydride affinities of the cations 1a, 2b, and 3b were also calculated.