Abstract: Material selection is one of the important steps in designing of oil production units. The reason is that this step affects on two important parameters: cost and effective design. The main concern of this study is the material selection for all important equipment like: flow lines, separators, tanks and others for an Iranian oil field which now is developing and it's construction is going on right now. The plant produces 50000 BOPD whereas the final treatment plant will produce about 165000 BOPD. The crude oil is sour and has high pressure (140 MPa) and temperature (about 100°C). The crude contains some corrosive elements like H2S, CO2 and water, of fluid coming from oil wells. For this reason the references that are used for this purpose are mainly NACE and API standards. For some equipment which work in sour area, according tso NACE-MR0175, some special alloys like Nickel alloys are used and for case of using carbon steels the amount of corrosion allowances is calculated.