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Graphical abstract Highlights • The designed setup is a useful tool for observing the oil-gas interfacial behavior. • The gas-oil interface of foamy oil was much more stable than that of nonfoamy oil. • The CO 2 -oil film exhibited the highest gas-oil interfacial stability. • Asphaltene properties had an important influence on foamy oil formation. • The asphaltenes from foamy oil contain a greater number of polar functional groups. Abstract Solution gas drive from some heavy oil reservoirs exhibits foamy oil behavior. However, the characteristics of oil that determine whether foamy oil behavior occurs have not been clarified. Therefore, we performed a comprehensive experimental study of gas-oil interfacial properties to provide more in-depth information about foamy oil formation. A new experimental setup for single film stability was designed to investigate the gas-oil interfacial stability and its influencing factors under reservoir conditions. Then, a series of micromodel experiments was conducted in high-pressure etched glass micromodels with foamy and nonfoamy oils to visually study the oil-gas interfacial stability in porous media. Finally, chemical characterization (acid and base number measurements, elemental analyses, nuclear magnetic resonance (NMR), and Fourier transformed infrared spectroscopy (FTIR)) was conducted to reveal the characteristic of foamy oil related to foamy oil formation. The results showed that the gas-oil interfacial stability increased at high oil component concentrations, small interfacial areas, and low temperatures. CO 2 -oil films exhibited higher gas-oil interfacial stability than N 2 and mixed gas (90 mol% CH 4 and 10 mol% CO 2) for both foamy and nonfoamy oils. A pressure at which the interfacial stability was minimized was observed. In addition, the gas-oil interface of foamy oil was much more stable than that of nonfoamy oil because the asphaltenes from foamy oil contain a greater number of polar functional groups (hydroxyl groups, carboxylic groups, amine, and heterocyclic rings), which adsorb at the oil-gas interface and increase stability. Therefore, a high asphaltene concentration with abundant polar functional groups could be the characteristic of oils responsible for foamy oil formation. [ABSTRACT FROM AUTHOR]