In air pollution meteorology, the height of the subsidence inversion, Zi, is a required parameter. This mixing height is needed because it provides the vertical extent for the airborne effluents to be dispersed. According to the Offshore and Coastal Dispersion (OCD) model, unstable conditions prevail when the Obukhov stability length (-L) is less than 25 m. This phenomenon occurs mainly in the afternoon during the peak of superadiabatic lapse rate. Because the routine timing of twice daily rawinsondings by the National Weather Service are 00 and 12 Z, direct measurements of Zi over the U.S. mainland are not available. As an alternative, hourly radar profiler measurements are employed. The U.S. Minerals Management Service has maintained such a station at Cocodrie, Louisiana near the north-central coast of the Gulf of Mexico. Examples of Zi measurements will be discussed. On the basis of extensive field experiments from the literature, we propose that Zi/(-L) = (2.9 + 288/(-L))^(3/2) can be used operationally for dispersion estimates such as the OCD model for both on- and off-shore environments.