Airlift pumps are simple devices using injected gas flow as the driving force for pumping liquids or a mixture of liquid and solid to higher levels. The pipe diameter, tapering angle of the upriser pipe, and submergence ratio are the most prominent parameters influencing the performance of airlift pumps. In this study, the performance of an air–water two-phase flow airlift pump with a tapered upriser pipe of 6 m height and tapering angle of 0.67° with inlet and outlet diameters of 60 mm and 200 mm is investigated experimentally. Experimental measurements for different submergence ratios ranging from 0.55 to 0.82 are utilized to investigate the effect of using a tapered upriser on the airlift pumping efficiency and void fraction. The results show that pumping efficiency of a tapered airlift pump is up to 40% higher than a constant diameter upriser airlift pump. In addition, it is found that the optimum level of submergence ratio for the tapered airlift pump is lower than the ordinary airlift pumps. The obtained improvement in pumping efficiency is described by illustrating the flow pattern map of the experimented airlift pump. It shows that the tapered upriser tends to keep the flow regime in the slug flow region which is assumed to be the best flow regime for airlift pumps. The behavior of void fraction in three different cross-sectional areas of the tapered upriser is represented using a drift flux model. The results show the reduction of void fraction as the cross-sectional area increases along the tapered upriser length.