Oligomers of methyllithium and tert-butyllithium (RnLin, n = 1-4; R = Me, t-Bu) as well as phenyllithium (PhnLin, n = 1,4) have been studied by using density functional theory (DFT). Possible conformers of methyllithium and tert-butyllithium oligomers were optimized at the B3LYP/6-31+G* level, and relative energies were evaluated at the B3LYP/6-311+G(2d,p)+ZPC//B3LYP/6-31+G* level. Optimized geometric parameters of MeLi and t-BuLi tetramers are in good agreement with available experimental and previous computational results. Atomic charges from natural population analysis (NPA) indicate that Li-C bonds show dominant:ionic character for methyl, tert-butyl, and phenyllithium oligomers. Comparison of atomic charges among the oligomers indicates that lithium charges are almost independent of the size of the:oligomer or the identity of the ligand. NBO second-order perturbation energy analyses for the T-d geometries of methyllithium and tert-butyllithium tetramers indicate that the hyperconjugative interaction (sigma (C-H) --> sigma*(-) (Li)) favors the eclipsed conformer relative to the staggered conformer. In particular, t-Bu4Li4 shows significant contribution to the hyperconjugative interaction from C-beta-H bonds as well as C-alpha-C-beta bonds. On the other hand, the phenyllithium tetramer prefers a staggered orientation of the phenyl ring to the C-Li bond due to similar hyperconjugative interactions in both orientations. Aggregation energies, computed at the B3LYP/6-311+G(2d,p)+ZPC//B3LYP/6-31+G* level, for the tetramers of methyllithium, t-butyllithium, and phenyllithium are -124.4, -108.6, and -117.2 kcal/mol, respectively.