Carbon steel is commonly used structural material for pipelines in oil and gas industry due to its economic feasibility. However, it is characterized by high susceptibility to corrosion attack and for this reason corrosion inhibitors are in majority of cases utilized to protect the steel. This paper investigates the interaction between quaternary ammonium compound-based inhibitor and carbon steel, C1020. The efficiency and impact of inhibitor on corrosion rate behavior of carbon steel was assessed through linear polarization resistance (LPR) under conditions representative in oil field. Carbon steel samples were tested in 1.5% NaCl with addition of inhibitor, purged with 1 bar CO2 at two different temperatures (25 °C and 75°C) and concentrations (10 and 100 ppm). Additionally, the prolonged immersion tests (120 h) were conducted. In spite of already established standard laboratory testing procedures, the aspect of divergent input values of testing parameters (scan rate, open circuit value) and its effect on electrochemical measurement results, has been limitedly discussed. Therefore, the influence of parameters of LPR method on corrosion rate values in combined inhibitor and carbon steel system was also evaluated and compared with standardized Tafel polarization method.