Kinetics of copolyesterification between poly(ethylene terephthalate) and 4-acetoxybenzoic acid (PET/ABA) in the melt has been analyzed using a phenomenological approach. A parallel second-order reaction sequence neatly summarizes catalyzed and uncatalyzed homopolyesterifications of 4-acetoxy benzoic acid (ABA) as well as the PET/ABA copolyesterification. Single stage kinetics fits the data reasonably well since the length of oxybenzoate sequences in the copolyester chain seldom exceed 5. Close correspondence exists between the kinetic parameters determined for the first stage of 4-acetoxybenzoic acid homopolyesterification, prior to oligomer precipitation, and those obtained in the present study through a least squares procedure. A Gauss-Legendre quadrature numerical procedure, used to compute the amount of acetic acid produced, is very efficient for comparison with experiments. Rate constants for copolyesterification are found to be several times lower than those of ABA polyesterification. The kinetics data support the formation of randomized blocks in the PET/oxybenzoate chain. The thermal data give support to this as well as to liquid crystallinity in a specific copolyester composition range. We also fitted a more elaborate complex kinetic model in which all the possible reaction sequences of importance have been explicitly accounted for. The complex rate model deviates from the simplified model by a marginal correction term. The simplified rate model directly results when we truncate the number of reaction events to only those few significant ones.