tert-Butylated phenols, which are important precursors in a variety of industries, are usually manufactured by reacting phenol in the presence of liquid acid catalysts, with pure isobutylene or C-4 fraction from naphtha crackers containing isobutylene. These processes suffer from problems associated with the use of highly corrosive liquid acids and also the source of isobutylene. In the current study, several solid acids, majority of which were based on montmorillonite K-10 clay, were evaluated with both methyl-tert-butyl ether (MTBE) and tert-butanol as alkylating agents in a pressure reactor under autogenous pressure. The activity of the catalysts was found to be in order: 20% (w/w) dodecatungstophosphoric acid (DTP)/K-10 > K-10 > 20% ZnCl2/K-10 > Al-exchanged K-10 > Zr-exchanged K-10 > Cr-exchanged K-10. The 20% (w/w) DTP/K-10 was found to be the most active catalyst with both MTBE and tert-butanol at 150degreesC and MTBE was a better alkylating agent. Effects of various parameters on rates and product distribution are discussed to deduce the kinetics of the reaction. A second order rate equation fits the data well under the assumption that both phenol and the alkylating agents are weakly adsorbed. The apparent activation energy was determined as 18.53 kcal/mol.