Absolute differential cross sections for neutral-neutral and charge—transfer collisions involving fast oxygen are presented. Neutral-neutral collisions are measured over the energy range 5-5eV, and between angles of .1 degrees and 5. degrees, while charge transfer measurements are presented for 15eV oxygen ions over the same angular range. A position sensitive detector is used to detect both the primary and scattered particles, yielding absolute differential cross sections. Target chambers with small ratios of length to exit aperture diameter are used and the end effects due to gas streaming out of the aperture are estimated by a Monte Carlo computer simulation. The excited state composition of the oxygen ion beam is considered, and differential cross sections for charge transfer are presented for both ground and excited-state oxygen ions.