The main objective of this paper is to develop synthetically new equations describing the sequential Burnett experiment including adsorption effects in the vessels. The usual Burnett analysis provides correct procedures for unadsorbing gases, which are adopted to minimize adsorption errors. The utility of the isothermal equations for adsorbing gases is demonstrated by reduction of steam data at the temperature of 498.15 K, by using a B.E.T. isotherm. Additionally, the Langmuir and the power series expansion models have been tested.