Ab initio calculations have been carried out in order to assign the bands observed in the carbon and oxygen K-shell spectra of gaseous tetrahydrofuran (THF), measured using inner-shell electron energy loss spectroscopy (ISEELS). The good agreement between the theoretical and the measured spectra allows us to re-assign precisely most of the peaks. The ionisation energies are calculated for the first time and found to be consistent with a quantum defect analysis of the core excitation energies. The calculated spectra for the C-2v, C-2 and C-s geometries of the molecule show very small differences. Thus, K-shell spectroscopy cannot be used to solve the controversy on the geometry of THF. (C) 2010 Elsevier B.V. All rights reserved.