The process where an ion in a magnetized plasma simultaneously absorbs two waves whose frequencies sum to the ion gyrofrequency may be referred to as double-cyclotron absorption as a source mechanism for oxygen (O+) conic distributions in the Earth's magnetosphere is investigated. The appropriate values of the relevant wave and plasma parameters are discussed and the applicability of approximate expressions for the average rate of perpendicular acceleration of O+ ions due to double-cyclotron absorption, derived by Ball (1989), is reviewed. The acceleration rate which results from the approximations of Ball (1989) is shown to be exactly a factor of 5 larger than the corresponding result of Temerin and Roth (1986). A possible explanation for this discrepancy is presented. Rough numerical estimates of the average rate of perpendicular acceleration of O+ ions along auroral field lines are considered, and it is shown that double-cyclotron absorption is indeed capable of producing O+ ions at energies comparable to those observed by spacecraft. ¿ American Geophysical Union 1989