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With the CO 2 flooding technique implemented, much CO 2 gas is dissolved in the produced fluid. A large amount of CO 2 escapes from crude oil due to continual depressurization in the surface pipeline system, leading to massive foam. In this paper, the effects of dissolved-CO 2 pressure and depressurization rate on foaming characteristics were investigated by depressurization. To explore the mechanism in depth, CO 2 solubility and interfacial characteristics were considered. The results indicated that foamability increases as the pressure increases and increases initially and then decreases with an increase in the rate. Further experimental results showed that when the pressure increases from 1.5 to 3.0 MPa at 30 °C, equilibrium interfacial tension decreases only by 12.78%, while CO 2 solubility increases by 81.73%, indicating that CO 2 solubility plays a dominant role in foamability. Additionally, it is inferred that when the rate is lower than 18 L/min, it increases at which point the gas that is originally dissolved inside the crude oil transforms to free gas. When it is increased above 18 L/min, the decrease in the solubility and enhancement of disturbance appear. These may be reasons why foamability decreases. Meanwhile, foam stability, the decay degree of foam height over time, was measured immediately after the foam height reached maximum. It was found that foam stability decreases when the pressure increases and increases initially and then decreases when the rate elevates. Further experimental results indicated that when the pressure increases from 1.5 to 3.0 MPa at 30 °C, the bulk viscosity and interfacial dilational modulus decrease by 23.45 and 38.58%, respectively. It is suggested that the role of interfacial viscoelasticity in foam stability is superior to that of viscosity. Additionally, it was inferred the increased rate below 18 L/min makes bubble size smaller, while the weaker structure of the foam film and higher surface energy make foam stability worse with the rate increased above 18 L/min.