A portable and submergible pressure sensor was developed in order to measure the axial pressure profiles in large-size industrial flotation columns. The system was used to evaluate the effects that operating variables, such as pulp density (1.1.-1.3 g/cm(3)), gas flowrate (1-2 cm/s) and interface level (0.2-2.5 m), have upon the pressure profile. It was found that local pressure varies with changes in pulp level, in the same order of magnitude that varies with common changes in gas flowrate and pulp density. These measurements show the large uncertainty in pulp level estimation using a single pressure sensor. Axial pressure profiles were estimated from different baffled section in large-size flotation columns. Typically, the data observed from different column sections showed an homogeneous gas distribution over the cross-section of the column. Local pressure measurement was used to estimate the axial gas hold up profile along the collection zone of large-size columns. A typical increase in gas hold up of 50-60(%), from the bubble generator up to the interface level was determined in industrial columns of 14-15(m) height and 1-16(m(2)) in cross-section. These data allowed the validation of models to estimate local mean bubble size. Average bubble sizes in the order of 0.9-1.3(mm), were estimated at superficial gas rates of 1.1-2.1(cm/s).