Six infrared bands of FO 2 have been measured at high resolution using a fast-flow long-path absorption cell and a Fourier transform spectrometer. The bands have been analyzed to obtain accurate band origins, as well as rotational, centrifugal distortion, and spin-rotation parameters. In order of increasing wavenumber they are ν3 at 579 cm -1, ν2 + ν3 at 940 cm -1, 2 ν3 at 1142 cm -1, ν1 at 1487 cm -1, ν2 + 2 ν3 at 1496 cm -1, and 2 ν1 at 2948 cm -1. Only ν3 has been studied previously (by C. Yamada and E. Hirota, J. Chem. Phys.80, 4694-4700 (1984)); the other bands are rotationally analyzed here for the first time. The ν1 and ν2 + 2 ν3 vibrations were found to be strongly mixed by Coriolis- and Fermi-type interactions and were thus analyzed simultaneously. 2 ν1 was also observed to be perturbed, but the perturbations were not analyzed. FO 2 now becomes one of the best-characterized unstable free radicals in terms of its rotation-vibration structure.