Int. J. Corros. Scale Inhib., 2015, 4, no. 2, 162 – 175 Some surfactants based on the vegetable oils as CO 2 corrosion inhibitors for mild steel in oilfield formation water V. M. Abbasov, 1 L. I. Aliyeva, 1 * Hany M. Abd El-Lateef 2 and I. T. Ismayilov 1 1 Mamedaliev Institute of Petrochemical Processes, National Academy of Sciences of Azerbaijan, AZ1025 Baku, Azerbaijan 2 Chemistry Department, Faculty of Science, Sohag University, Sohag, Egypt *E-mail: leylufer-ipcp@rambler.ru Abstract The new complex surfactants were synthesized based on sunflower oil and its inhibiting action on the corrosion of carbon steel in CO 2 -saturated oilfield formation water was investigated by means of weight loss and linear polarization resistance corrosion rate. The results revealed that the studied surfactants were excellent inhibitors. The percentage inhibition efficiency (IE %) increases by increasing the inhibitor concentration until the critical micelle concentration (CMC) is reached. The strong adsorption ability of the surfactant molecules leads to formation of a mono-layer, which isolates the surface from the environment and thereby reduces the corrosion attack on the surface. The adsorption process was found to obey the Langmuir adsorption isotherm. Keywords: carbon steel pipelines, corrosion, complex surfactants, adsorption isotherm, weight loss measurements, oilfield formation water. Received: February 12, 2015. doi: 10.17675/2305-6894-2015-4-2-162-175 1. Introduction Corrosion in the oil industry represents one of the major problems. Carbon steels are extensively used in oil industries, i.e., C1018 carbon steel is one of the most common material used as tubing in oil well. However, carbon steels are susceptible to corrosion in environment containing oil production. It has been acknowledged that CO 2 corrosion is one of major corrosion types resulting in oil well failure [1]. Due to the complexity of environment in oil well, CO 2 corrosion is dependent on various environmental conditions like temperature, CO 2 partial pressure, flow conditions and protective corrosion scales [2 – 7]. Corrosion inhibitors are the most effective and flexible mean of corrosion control in oil and gas production systems, but the selection and application of inhibitors are actually complicated because of the variable corrosive environments in these systems [8]. Many organic compounds containing oxygen, nitrogen and sulphur atoms have been used as corrosion inhibitors for carbon steel in various aggressive environments [9 – 14]. The addition of high molecular weight organic compounds such as surfactants to combat