This paper deals with the esterification kinetics of oleic acid (OA) using ethanol (EtOH) over acrylic-supported lipase from Aspergillus niger (Novozym 435) as catalyst. The reaction was carried out in a stirred 500 mL Pyrex glass reactor at 45oC under conditions with negligible external and internal transport resistances. Reaction runs in a microaqueous medium employed OA: EtOH ratio, b, between 0.01 to 2.0 without initial addition of water. The rate dependency on reactant concentration has a maximum at b=0.9, just below the stoichiometric ratio, and was therefore described by a Michaelis- Menten kinetic expression implicating irreversible surface reaction between adsorbed OA and EtOH as the rate-controlling step. Ethanol inhibition was significant in this monophasic medium. Although there is no literature agreement on the optimum water content in the biphasic system, the existence of multiple peaks in the sinousoidallydecaying rate-water content profile over a wider range (0 to 26.5wt%) than previously investigated is symptomatic of an autoregulatory behaviour between the organic and aqueous phases. This was ascribed to the dynamic migration of ethanol between the well-mixed water and organic pools leading to periodic states in enzyme revivification. The oscillatory kinetics was adequately fitted to under-damped sinusoidal expression with model parameters related to the resonant frequency of the open-close waterassisted activation of the lipase site.