OH formation has been observed directly from the reaction between CH3CO and O2. This reaction proceeds via the formation of energised CH3CO(O2), which can either dissociate to OH or be collisionally stabilized to CH3CO(O2). The kinetics of OH formation were measured as a function of pressure at 295 and 213 K, giving rate coefficients in good agreement with the literature. The OH yield was also determined as a function of pressure enabling the reaction to be further quantified.