A batch reactor was employed having pH meter, IR probe and continuous operation detectors so that it could work as a CSTR reactor. As esterification advanced, then IR bands corresponding to the carboxyl acid COOH group and the alcohol C-OH group decreased whilst a parallel increase was presented in the ester -COOR group band which was forming. Reaction progress could be observed by continuous IR spectrum registration. The IR band for HOH (water) could not be studied because it needed a completely anhydrous medium for doing so. Standard solutions could be prepared for quantifying IR band peak intensity, according to a component's composition in the mixture. However, when phase changes occurred in the reaction mixture, this method could not be employed for following the course of a particular reaction because random variation was detected in band intensity.