The major factor determining gas injection effects and the type of injected gas is the variation of volatile oil properties during the process of injecting gas into a volatile oil reservoir. By use of the fluid from a typical inland volatile oil reservoir, four gas⁃es including CO2, N2, CH4 and natural gas are injected into the volatile oil separately by means of swelling experiments after phase behavior experiments are well-fitted. The comparison of the effects of the four gases on the volatile oil properties has been studied. And in order to verify the accuracy of the swelling experiments, a mechanism model is created to simulate the development effect of injecting different gases into the reservoir. The results show that CO2 has no effect on the saturation pressure of the volatile oil un⁃der the same injecting rate. At the same time, the degree of volume expansion and interfacial tension reduction is largest when in⁃jecting CO2 into the oil and it reduces the viscosity to a certain extent. CO2 is the ideal gas for the volatile oil reservoir in the pro⁃cess of gas injection. While considering the difficulties of CO2 source accession and pipe anticorrosion, natural gas is a substitute gas which is economical and effective.%挥发性油藏在注气过程中的流体性质变化是决定注气效果以及确定注入气类型的主要因素。为此，以国内某典型挥发性油藏流体为例，在相态实验拟合的基础上通过注气膨胀实验对比了四种气体（CO2、N2、CH4、天然气）注入对挥发油流体性质的影响，同时为了验证注气膨胀实验结果的准确性，建立机理模型模拟了注入不同气体的开发效果。结果表明：在相同的注入气比例下，CO2对挥发油饱和压力基本没有影响，使体积膨胀和界面张力降低幅度最大，同时降黏效果也较好；CO2是挥发性油藏注气保压开发最理想的气体，若考虑到注CO2在气源获取和管材防腐等方面存在困难，则天然气是另一种可选择的经济有效的气体。
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