New strategies are required in the study of gas exchange under energetic and changeable conditions where current techniques are limited, especially in their ability to represent the contribution of injected bubbles. We have developed a gas tension device (GTD) that uses a solid-state differential pressure sensor to make continuous in situ measurements of the difference between pressure of dissolved gas (gas tension, for succinctness) and pressure of gas in the gas phase above a water parcel. This information allows the determination of the rate of approach to a dynamic equilibrium and of the degree of water phase saturation at steady state. The method is demonstrated in the lab by following the invasion of CO2 into seawater with bubble injection. The GTD introduces a new and versatile measurement method for the study of gas transfer across air-water interfaces, one which avoids many of the sampling and bias problems of traditional approaches. ¿ American Geophysical Union 1992