Developing a giant field is a challenging task; the main goal is to reach to the highest ultimate oil recovery (UOR) by finding the best locations for new producers and injectors. Besides, converting existing producers to injectors and vice versa are other ways to increase the recovery. Hence, in this approach, we use combination of infill drilling and converting producer well to injector so as to maximize UOR. Lots of methods are recommended to develop fields, but none of them is comprehensive enough. To develop a field, the location of a new well should be considered and then its effect on the ultimate production should be investigated. This approach normally deals with testing hundreds or thousands of potential infill alternatives by numerical simulations which is a very time consuming and expensive process. One of the newest methods to develop a field is using streamline simulation. In this approach, we suggest two main stages; first to gain the most possible advantages from the infill drilling, new producers should be drilled in sections of the reservoir where the streamline density is low and the oil saturation is high. Second, converting mostly dead producers to injectors could be a very useful method based on the density of the streamlines around the old producers. We used the method to develop a complicated reservoir. For this reason, we used grid-base and streamline simulation to verify the outcomes. The results show that UOR increases around 70 percent by infilling and switching the producers to injectors. In this work, we use the streamline approach to develop a guideline to drill new producers and switch some of the old producer wells to injectors in order to increase the oil recovery. This method could compete favorably with EOR processes on a recovery basis for much less investment and operating cost.