The geometric structure and conformational properties of trifluoromethyl chlorosulfonate (chlorosulfuric acid trifluoromethyl ester), CF3OSO2Cl, have been detd. by X-ray crystallog., gas electron diffraction (GED), and vibrational spectroscopy [IR (gas), IR (matrix), and Raman (liq.)]. These exptl. investigations were supplemented by quantum chem. calcns. (B3LYP with 6-311G* and 6-311+G(3df) basis sets). All exptl. methods result in a single conformer with gauche orientation of the CF3 group relative to the S-Cl bond. The dihedral angle d(COSCl) is detd. to be 91.7(3) Deg in the crystal and 94(3) Deg in the gas phase. This dihedral angle corresponds to a near-eclipsed orientation of the O-C bond relative to one of the S:O double bonds (d(CO-SO) = -23.0(3) Deg and -21(3) Deg in the crystal and gas phase, resp.).