In a process for producing phenol and cyclohexanone, reaction components comprising cyclohexylbenzene hydroperoxide and an acid catalyst are supplied to a cleavage reaction zone, mixed under mixing conditions effective to combine the reaction components into a reaction mixture and at least part of the cyclohexylbenzene hydroperoxide in the reaction mixture is converted under cleavage conditions to into phenol and cyclohexanone; and a cleavage effluent is recovered from the cleavage reaction zone. The cleavage and mixing conditions are controlled such that the ratio tR/tM is at least 10, where tR is the half-life of cyclohexylbenzene hydroperoxide under the cleavage conditions and tM is the time required after injection of a tracer material into the reaction mixture under the mixing conditions for at least 95% by volume of the entire reaction mixture to attain at least 95% of the volume-averaged tracer material concentration.