The reaction of phenol carboxylation with alkali metal salts of ethyl carbonic acid was studied. It was found that phenol carboxylation with sodium ethyl carbonate under optimal conditions (P-Ar = 1 MPa, T = 200degreesC, tau = 6 h) yielded o-hydroxybenzoic acid (69.9%) and p-hydroxybenzoic acid (17.5%). A simple and convenient method for the preparation of p-hydroxybenzoic acid by phenol carboxylation with potassium ethyl carbonate (P-CO2 = 2.5 MPa, T= 210degreesC, and tau = 7 h) in a 71% yield was developed.