The effect of varying mobile-phase pH and percent methanol on the reversed-phase HPLC separation of benzoic acid and phenol is investigated. Both analytes are of interest owing to their classification as moderate environmental and health hazards. Baseline separation of the analytes is observed in five of the nine mobile-phase compositions studied. At low levels of methanol, as pH increases, the elution order of the benzoic acid and phenol peaks reverses. A similar trend is observed at intermediate levels of methanol. At high levels of methanol, as pH increases, the two-component sample begins to resolve, but baseline resolution is never achieved. In general, as percent methanol increases, the retention time of both analytes decreases. This is independent of mobile-phase pH.