We investigate uniform gas injection using a needle sparger as a structuring methodology to reduce backmixing in slurry bubble columns. Using optical probes, we determined the gas fraction and the bubble behaviour in 2D and 3D slurry bubble columns with a uniform gas injection. Experimental results for air-water-glass beads (d(s) = 1081 mu m, U-sg = 0-0.10 m/s) indicate that a strong reduction in the vortical structures has been achieved and the homogeneous flow regime can be extended beyond 30% gas fraction. Increasing the solids concentration decreases the gas fraction and widens the bubble velocity distribution. Furthermore, we show by modelling that the reduced backmixing leads to a major improvement of the conversion in case of Fischer-Tropsch synthesis.