This paper investigates the phase behavior and mutual interactions between a light crude oil and CO₂ at high pressures and high temperatures (HPHT). To do so, we have measured PVT properties of the CO₂-oil system at HPHT using a PVT setup. We have also tried to present a detailed methodology for measuring PVT properties of CO₂-oil systems and highlight the difficulties such as oil vaporization by CO₂ during the experiments. A crude oil sample, collected from a Malaysian oil field, was used here. Our experiments indicated that, CO₂ solubility in the oil increased at higher pressures when measured at a fixed temperature. Our experiments also showed that increasing the test temperature would reduce CO₂ solubility in the oil, while its effect is more significant at higher pressures. The swelling factor (SF) measurements showed an increasing trend with pressure up to a certain value so-called extraction pressure, at which, the SF started to be reduced even became less than one. The measurements of oil viscosity indicated that CO₂ dissolution in the oil sample could reduce the mixture viscosity up to 61%. The interfacial tensions between CO₂ and the crude oil at different pressures were also measured while the results were used to estimate the minimum miscibility pressure (MMP) and the first contact miscibility (FCM) pressure. The IFT measurements at various pressures displayed a reduction trend as a result of more CO₂ dissolution in the oil but with two different slopes. That is, at lower pressure values, the measured IFTs were sharply reduced with pressure, while the reduction rate of the IFT became less when pressures exceeded the extraction pressure. This study helps with determining the optimum pressure and temperature conditions of CO₂-oil systems to have a minimum IFT, a maximum CO₂ solubility and SF, and a minimum oil viscosity that are favorable for CO₂-enhanced oil recovery projects. Additionally, the methodology presented here gives guidelines on how to design PVT experiments of CO₂-oil systems for petroleum and chemical engineering applications.