Oxygenated fullerenes anions were produced by a vaporization source equipped with a corona discharge ionizer in the presence of a trace amount of oxygen. In situ mass analysis revealed that the species formulated as C60On- (n less than or equal to 30) were formed in the source and that the degree of oxygenation could be altered by the discharge current. Formation of the epoxide structure in the C60On- was suggested by XPS measurements for thin films prepared by deposition of the C60On- beam. The structures and formation processes of higher analogues (C60)(m)O-n(-) (m = 2, 3) are briefly discussed. (C) 2003 Elsevier B.V. All rights reserved.