Trimethylolpropane esters (TMPE) is very interesting lubricant because its thermal-oxidative stability, low pour point, low volatility and biodegradability. In this research, the effect of various factors on % conversion and selectivity in esterification of trimethylpropane (TMP) and octanoic acid using sulfated zirconia as acid catalyst were investigated. The effects of time (1-8 hr), temperature (90-150℃), Octanoic acid: TMP molar ratio (3:1-5:1), catalyst loading (0-10% w/w octanoic acid) and supercritical CO₂ were studied. The % conversion and selectivity were analyzed by gas chromatography (GC) and the catalysts were characterized by thermogravimetric analyzer (TGA). It was found that % composition of reaction mixture and product selectivity increased when reaction time, temperature, Octanoic acid: TMP molar ratio and amount of catalyst were increased. The complete reaction was observed at 8 hour, 150℃, 5%w catalyst and 4:1 octanoic acid :TMP molar ratio. For supercritical carbon dioxide, effect of density is very important factor to increase solubility of reactants and products in supercritical CO₂.