The effects of temperature and pressure on interfacial tension (IFT) of a CO₂/n-pentane binary system were investigated using the pendant drop method. To ensure the accuracy and reproducibility of our results, the pendant drop method is first used to measure the IFT of fluid systems whose results are available in the literature and then the validated experimental procedure is applied to determine the IFT of the CO₂/n-pentane system as functions of pressure (ranging from 0.18 to 6.07 MPa) and temperature (ranging from 296.15 to 377.55 K). Within the pressure and temperature ranges applied, IFT values varied from 0.94 to 15.2 mN/m, and it is observed that IFT decreases monotonically with isothermally increasing pressure; however, when the temperature increases isobarically, IFT decreases at low pressures but the trend reverses at higher pressures, where IFT shows greater values at higher temperatures than at lower temperatures. Modeling of the experimental IFT results using the parachor equation for the binary mixture is also discussed.