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Gas holdup and liquid circulation velocity are amongst the most widely studied parameters in airlift reactors. This emphasis attests to their significance. The difference in gas holdup between the riser and the downcomer in an airlift reactor determines the magnitude of the induced liquid circulation velocity which in turn influences the bubble rise velocity, and the gas holdup. The holdup and the liquid velocity together affect the mixing behaviour, mass and heat transfer, the prevailing shear rate, and the ability of the reactor to suspended solids. Clearly, all aspects of performance of airlift systems are influenced by gas holdup and liquid circulation. Because of its significance, the relationship between the gas holdups in the riser and the downcomer has received some attention in the published literature. Almost all existing relationships between the riser and the downcomer gas holdups in airlift devices were purely …