Experimental measurements of gas phase hold up in two phase gas-liquid cocurrent upflow packed bed reactors have been made at very low gas ((N(Re))(g) < 55) as well as liquid ((N(Re)1 < 8) velocities using air- water systems with two different types of packing materials. The gas hold up values thus obtained are correlated in terms of Re(g), Re1 and ε, the voidage.