The threshold behavior of the cross-section for positive ions formed via electron impact ionization of propane (C 3 H 8 ) 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).