Modeling of flotation has been the subject of many investigations aiming at better understanding the process behavior per se, and as well for process design, control and optimization purposes. With this regard, the importance of hydrodynamic characteristics, either as manipulated or measured variables, are paramount. The interfacial area of bubbles (I-b) is introduced in Part 1 of this paper as a hydrodynamic variable providing more information about the size distribution than the commonly used bubble surface area flux (S-b). Experimental evidence shows that the bubble size distribution can exhibit normal, lognormal, and even multi-modal shape. Unlike the Sauter mean diameter (d(32)) and S-b, the interfacial area of bubbles is derived from the complete bubble size distribution, and takes into account these specific characteristics. Fundamental expressions are proposed to allow characterising I-b using the population mean and standard deviation. Experimental results indicate that for lognormal bubble size distributions, I-b correlates well with the gas hold-up and d(32). Part 2 of the paper analyzes the correlation of gas dispersion characteristics with flotation rate constant. (C) 2014 Elsevier Ltd. All rights reserved.