The threshold behavior of the cross-section for positive ions formed via electron impact ionization of propane (C3H8) has been studied in a crossed electron/neutral beams apparatus with mass spectroscopic analysis of the ions. Appearance energies (AEs) for two states (C-s and C-2v) of the parent ion C3H8+/C3H8 (AE(C-s) = 10.51 +/- 0.05 eV and AE(C-2v) = 10.96 +/- 0.05 eV) and for six additional fragment ions have been determined. Moreover, for the four most abundant cations appearance energies have been measured at two different temperatures (290 and 690 K) showing a decrease of the appearance energies with increasing gas temperature. The present experimental results are compared with appearance energies calculated using high level quantum chemical methods (G3, G3B3 and CBS-QB3). (C) 2004 Elsevier B.V. All rights reserved.