The conformational space of 3-buten-2-ol (BUO), governed by the torsion angles phi (1)(O-C-C=C) and phi (2)(H-O-C-C(sp(2))), was searched, and nine energy minima were located, using the B3LYP/6-31**G approach. Then, geometries of these nine and the vibrational characteristics of the four lowest energy forms were calculated. Experimental evidence of the latter four conformers in the gas phase was obtained from IR frequencies, band intensities, and band shapes measured at room temperature. Analysis of electron-diffraction intensities also measured at room temperature gave the following abundancies (with nomenclature pertinent to the S configuration): (+ac, -sc), 58%; (sp, -sc) and (sp, +sc) together, 32%; (-ac, Ssc), 10%. The energy sequence as well as conformationally induced variations in bond lengths, valence angles, and OH frequencies could be rationalized by attractive (hyper)conjugative and repulsive steric effects operative in BUG. The intermediacy of BUO between allyl alcohol and I-butene shows in the observation that C2-H, C2-OH, and C2-CH3 eclipse the C=C bond in the (+ac, xx), (sp, xx), and (-ac, xx) conformers, respectively. In all four conformers, OH points toward C=C, indicative of an attractive intramolecular OH/pi (C=C) interaction. Experimental and calculated wavenumbers of the individual conformers could be matched satisfactorily, after scaling the four B3LYP force fields using only three transferable scale factors published by Rauhut and Pulay.