This paper describes the effective boundary conditions for the gas dispersion parameters of bubble size, superficial gas velocity and bubble surface area flux, in mechanical and column flotation cells. Using a number of previously derived correlations, with appropriate simplifying assumptions, and experimental data reported from plant practices, the boundary conditions were identified. Thus, it was shown that these constraints typically allow for a mean bubble diameter range of dt, 1-1.5 mm and superficial gas rate of J(g) = 1-2 cm/s, in order to maximize the bubble surface area flux, S-b = 50-100 s(-1). Under these conditions there is no carrying capacity limitation, while keeping a distinctive pulp-froth interface. (C) 2007 Elsevier Ltd. All rights reserved.