The chemical equilibrium of the reactive systems (alkanol + methylbutenes <----> alkyl tert-amyl ether) with the following alkyl substituents: ethyl, propyl, butyl, iso-propyl, see-butyl, and cyclohexyl, were studied in the liquid phase. Reactions were investigated in the screwed vials in the temperature range (298 to 393) K, and a cation exchanger Amberlist 15 was used as heterogeneous catalyst. Enthalpies of reactions Delta(r)H(m)(o) of tert-amyl alkyl ethers synthesis in the liquid phase were obtained from the temperature dependence of the equilibrium constants and used to derive standard enthalpies of formation, Delta(f)H(m)(o)(1), of tert-amyl alkyl ethers. For the sake of comparison, these enthalpies of formation have been calculated using improved Benson's increments. Calculated values are in close agreement with those from thermochemical measurements.