Local average bubble size in a dual turbine stirred tank is investigated. Results ate compared with data from the literature, obtained under many different conditions, including different types and numbers of stirrers, different media and measuring systems. For Rushton turbines, bubble size increases from the stirrer tip along the discharge stream, soon to reach a value representative of the bulk of the tank, near the tank wall. This is common to coalescing and non-coalescing systems. Differences in d(32) cannot be clearly attributed to size of tank, number or type of stirrers or measuring method. Dispersion within each author's data is at least as significant as the differences between authors. Bubble sizes in electrolyte solutions are smaller and more sensitive to power input than in water. Surfactant addition results in a further decrease in bubble size. Data may be correlated by d(32) = C"(P-g/V)(beta) with exponent beta decreasing from (-0.52) near turbine to (-0.37) bulk for non-coalescing media and from (-0.24) near turbine to (-0.14) bulk for coalescing media. The effect of gas flowrate on d(32) is not detectable, except near the turbine for coalescing media. To correlate data under the se conditions, the effect of gas loading must be included.