Relative populations of four IPR (isolated-pentagon-rule) isomers of Eu@C-82 are computed using the Gibbs energy based on characteristics from density functional theory calculations (M06-2X/6-31G*similar to SDD entropy term, M06-2X/6-31+G*similar to SDD or B2PLYPD/6-31G*similar to SDD energetics). Only the species observed by now also show significant calculated populations. A role of solubility in different solvents and/or composition of the arc electrodes could explain variability in the observed populations.