Annotation. Corrosion leads to huge losses every year, and solving this problem is an important task. One of the effective methods of corrosion protection of equipment and pipelines in the oil industry is the use of corrosion inhibitors. Inhibitory protection is the most technological and effective way to control corrosion of oilfield equipment. The article deals with phosphate corrosion inhibitors of complex action in a carbon dioxide environment. The method of corrosion testing is generally accepted. Quantitative indicators of corrosion processes were calculated using formulas, and the measurement uncertainty was estimated using an algorithm using the Student's coefficient with a confidence probability of 0.95. In the course of the work, potentiometric determination of the pH of corrosive media using a combined glass electrode and an ionomer, conductometric and photocolorimetric determination of the content of iron (III) with potassium rhodanide, as well as methods of infrared spectroscopy and electron microscopy were carried out.