The cross-sectional gas hold-up profiles in three bubble column reactors (BCR) with different aspect ratios and sparger types were obtained using electrical resistance tomography for nitrogen-water system. Two acrylic BCRs (0.09 and 0.17 m ID with heights 1.61m and 1.15m respectively) with sintered plate spargers and a stainless steel BCR (0.15 m ID, height 0.90 m) with a mesh sparger were used to compare radial and centreline hold-ups. Fractional gas hold-up was found to lie between 0.02 and 0.15 and was generally higher for the 0.09 m ID BCR as a result of bubble break-up and bubble-wall collisions. For the columns with sintered plate spargers at 14 LPM of nitrogen, radial profiles obtained at two axial locations (H/D = 1.1 and 3.5) showed larger hold-up for 0.09 m ID column compared to the 0.17 m ID column. Comparison of hold-ups between sparger designs at H/D ratios of 1.1 and 3 showed that the stainless steel BCR achieved higher hold-ups compared to the 0.17 m ID column due to bubble coalescence and larger drop in mixture conductivity as the gas rise upwards in the column. The drop in the mixture conductivity close to the sparger was higher at low flow rates, indicating that the bubbles are uniformly distributed. The centreline hold-up increased as the H/D ratio increased and can be correlated by power-law models. Heterogeneity Index for pixel-based Tomograms Statistic was used for flow regimes identification (bubbly or churn-turbulent flow) in BCRs using different patterns in the pixelated images.