The molecular structures of the vapors produced on heating dimethylalkoxygallanes of the type [Me2Ga(OR)](2) have been determined by gas electron diffraction and ab initio molecular orbital calculations. In the solid state [Me2Ga(OCH2CH2NMe2)](2) (1) and [Me2Ga(OCH2CH2OMe)](2) (2) adopt dimeric structures, although only the monomeric forms [Me2Ga(OCH2CH2NMe2)] (1a) and [Me2Ga(OCH2CH2OMe)] (2a) were observed in the gas phase. For comparison the structure of the vapor produced on heating [Me2Ga((OBu)-Bu-t)](2) (3) was also studied by gas electron diffraction. In contrast to 1 and 2, compound 3 is dimeric in the gas phase, as well as in the solid state. The gas-phase structures of la and 2a exhibit five-membered rings formed by a dative bond between Ga and the donor atom (N or O) from the donor-functionalized alkoxide. In 3 there is no possibility of a monomeric structure being stabilized by the formation of such a dative bond since only a monofunctional alkoxide is present in the molecule.