First time electron spin resonance studies are reported for various isotopomers of GaH2 and HGaCH3. The radicals were generated in neon matrices at 4 K by the ultraviolet photoexcitation of Ga which undergoes insertion reactions with H-2 and CH4. Ab initio calculations with a large uncontracted basis and configuration interaction with all single excitations from the spin-restricted Hartree-Fock configuration gave good agreement with the experimental results and supported the free atom comparison method interpretation of the hyperfine interactions. A comparison with similar radicals is presented, including BH2, AlH2, HA1CH(3), HA1OH, and A1H(+).