Relative concentrations of seven isomeric C-72 cages (one species with isolated pentagons, two isomers with a pentagon-pentagon junction, a cage with a heptagon, a cage with two heptagons, and two isomers each with two pentagon-pentagon fusions) are computed using the Gibbs energy in a broad temperature interval. It is shown that the non-IPR C-2v cage with one pentagon-pentagon junction prevails at any relevant temperature. Although the IPR-satisfying structure is the second lowest in energy, it is disfavored by entropy so that several cages still higher in energy are in fact more populated at higher temperatures. (C) 2003 Elsevier B.V. All rights reserved.