The success of the hydrocarbon recovery improvement via Water Alternative Gas injection process is closely related to the microscopic displacement and macroscopic sweep efficiency. Effectiveness of the successive displacements by water and gas injections, maximizing the three phase zones by optimum force balancing in the reservoir, WAG injection cycle, double displacement and film drainage process are among the important parameters that affect the sweep and displacement efficiency in WAG process. Water and gas injection scheme play an important role in optimization of these parameters. Different schemes of WAG injection have been reported in open literature including gas injection up dip, water injection down dip and vice versa. In this paper, the efficiency of various WAG injection schemes toward improvement of the above important parameters will be presented. Detailed theoretical investigation and simulation study are conducted. A new injection scheme is proposed. In the proposed methodology, water is injected from down dip and gas is injected from up dip in the first cycle. In the second cycle, gas is injected from down dip and water is injected from up dip. Water and gas injection location will alternatively change in each cycle of injection. Different design parameters are considered and studied including mobility ratio between water and oil phases, location of the water and the gas injectors, injection rate, WAG injection cycle. The results show that the proposed methodology has significant improvement on the displacement efficiency and three phase zone size and hence yield higher hydrocarbon recovery. Copyright 2011, Society of Petroleum Engineers.