Abstract: Terephthalic acid is esterified with an alkylene glycol by heating in a first stage one mole of the acid with at least about 1.2 moles of the glycol and 0.01 to 1.0% based on the weight of the acid of a volatile organic base at a temperature between 240.degree. and 320.degree. C and at a pressure above the vapor pressure of the glycol at the reaction temperature until about 75-85% of the acid groups initially present in the terephthalic acid have been esterified, and then maintaining the reaction mixtures from the first stage in a second stage at a temperature between 240.degree. to 320.degree. at a pressure less than that of the said first stage until at least about 95% of the acid groups initially present in the terephthalic acid have been esterified.