The effect on oligomerization of increased steric bulk in dimethylindium(III) chalcogenolates (Me(2)InER') (E = O, S, Se) has been examined. The facile reaction of Me(3)In with a series of phenols, thiophenols and selenophenols afforded the compounds [Me(2)InO(C(6)H(5))](2) (1), [Me(2)InO(2,6-Me(2)C(6)H(3))](2) (2), Me(2)InO(2,4,6-tBu(3)C(6)H(3)) (3), [Me(2)InS(C(6)H(5))](infinity) (4), [Me(2)InS(2,4,6-tBu(3)C(6)H(3))](infinity) (6), [Me(2)InSe(C(6)H(5))](2) (7), [Me(2)InSe(2,4,6-Me(3)C(6)H(3))](infinity) (8) and [Me(2)InSe(2,4,6-tBu(3)C(6)H(3))](infinity) (9). All compounds have been characterized by elemental analysis, melting point, FT-IR, FT-Raman, solution NMR, and X-ray crystallography. The structures of 1-2 are dimeric via short intermolecular In-O interactions, yielding a symmetric In(2)O(2) unit and a distorted tetrahedral C(2)O(2) bonding environment for indium. Increasing steric bulk in 3 results in the isolation of a monomeric species, exhibiting a distorted trigonal planar C(2)O bonding environment for indium. In contrast to 1, the thiolate analogue 4 exhibits a polymeric structure via mu(2)-SPh groups and a distorted tetrahedral C(2)S(2) bonding environment for indium. Increasing steric bulk resulted in the formation of a chain of weakly coordinated monomers via intermolecular In...S interactions in [Me(2)InS(2,4,6-tBu(3)C(6)H(2))](infinity) (6). Although 7 shows a dimeric species similar to 1, the 2,4,6-trimethyl substituted selenolate analogue 8 exhibits a polymeric structure, while the -Se-2,4,6-tBu(3)C(6)H(3) analogue (9) showing a similar structure to 6. Comparison to previously reported structures of diorganoindium chalcogenolates demonstrates the importance of the methyl substituents on indium in facilitating the isolation of higher (non-dimeric) oligomers. Theoretical calculations demonstrate the significance of altering the R and R' groups and E on the degree of oligomerization in [R(2)InER'](n) species.