Air-lift reactors are important gas-liquid contactors for gas separation, purification, fermentation and waste water treatment on account of their simple construction and low energy consumption together with high mass and heat transfer rates. Apart from the improved liquid mixing, air-lift reactors have no moving elements and the power requirement comes only from the air supply. A new air-lift tube (ALT)-type reactor was investigated in laboratory and pilot scale. A study was conducted to measure the effects of liquid properties (such as viscosity and density) on the hydrodynamics of the ALT reactor. The systems used for this study were: air/water, air/sodium hydroxide solution, air/sodium citrate buffer solution and air/glycerine. Pressure drop in the reaction tube, minimum and maximum gas velocities, pressure frequency and recycle liquid velocity in the recycle tube were measured under different experimental conditions using different tube diameters for the recycle and reaction tubes. Design correlations for the above-mentioned parameters were developed by computer program in order to design an ALT reactor for gas-liquid reactions. The correlations are valid in the range 0.1-1400 m3 h-1 of the gas stream.