The energy of the reservoir uses to rise the production to the surface from natural flowing wells. The energy source is the reservoir pressure. The pressure that makes the crude oil from the reservoir flow to the bottom of the well is known as the flowing bottom hole pressure. When bottom hole flowing pressure is relatively high, the pressure can raise the oil to the wellhead, and even into the gathering manifolds and the separator. In addition, with the rising oil and gas flowing along the wellbore, the pressure will gradually reduce, and the gas will be separated out and expand its volume. This study focusing on the determination and analysis of the natural flow characteristics for four wells in Intesar oil field using PIPESIM software. The data and main tools for this study have been gathered and prepared for the completion of the calculations which include: the PVT data analysis, well completion configuration, well model and results investigation for the build of the natural production system network from the reservoir to the separator. Sensitivity analysis will be applied for this study to optimize the best operation properties. The main findings from this analysis are that, increasing tubing inside diameter results in increasing of the maximum value of the flow tare but this value must not exceed the value of the erosion velocity of the pipeline line material. Also, software calculation gives more accurate results than the manual calculations.