The reactivity of phenol under noncatalytic conditions with propionaldehyde, acetone, and propionic acid were determined in the presence of water at supercritical conditions and in the absence of water at 673 K. The reaction of phenol with propionaldehyde gave alkylphenols in supercritical water. The yield of the alkylphenol products and ratio of para isomers to ortho ones increased with increasing water density. Over the range of reaction conditions studied, acetone showed no reactivity with phenol regardless of whether water was present or not. The reaction of propionic acid with phenol yielded the corresponding ester in the absence of water.