In this paper, we focus on the interfacial properties, relative volume change, and PVT behavior of CO2 and CH4 in (w/ho) emulsions, which is encountered in heavy oil reservoirs during secondary recovery methods such as water or steam injection. We generated the water-in heavy-oil (w/ho) emulsion using steam at 150 degrees C for two types of oils (27,000 cP and 4351 cP). Next, the stability of our emulsion was tested using different criteria such as phase separation, viscosity of the produced emulsion compared with that of the starting oil, and the size and number of water droplets in the continuous medium. The influence of water content in the emulsion was found to be critical and thus subsequent surface tension (SF) and relative volume measurements as well as PVT analyses were conducted using emulsions of different water contents with a vol.% range from 10 to 70. SF and volume measurements indicate the existence of critical water content which dramatically changes the behavior of the system; generally, emulsions with water content below this critical value exhibit lower SF than the original oil, and the SF falls steadily as the water content increases. The trend is reversed when the water content exceeds the critical value and SF starts increasing before it stabilizes. This process happens when the water content reaches a vol.% higher than 50; however, it remains below that of the original oil. Volume ratio increases as pressure increases regardless of water content. For experiments run with CO2, data suggests that water content affects the rate of expansion, but ultimately the final volume ratio remains the same. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.