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Glyoxal is a potential sequestrant of H 2 S in the pre-salt exploration. However, the mixture containing packer fluid and glyoxal is corrosive. The addition of an eco-friendly polyol phosphate acts as corrosion inhibitor of the AISI 1020 in this environment. The objective of the present work was to study the influence of phosphate content in the inhibitor formulation, as well as its action in packer fluid and glyoxal solution in the presence of dissolved CO 2 , by means of surface analysis and electrochemical measurements. The results demonstrated that the inhibition efficiency increases as the phosphate content increases. In the beginning of the tests, the polarization resistance increases from 2.2 kΩ cm 2 (2.5 % phosphate) to 11.2 kΩ cm 2 (10 % phosphate). In CO 2 – containing medium, 500 ppm dosage of polyol phosphate increases the polarization resistance (from 0.35 kΩ cm 2 to 5.9 kΩ cm 2 ) and decreases both the capacitance (from 111.5 μF cm -2 to 10.2 μF cm -2 ) and the corrosion current (in 67%). Polyol phosphate is effective as corrosion inhibitor in the presence of CO 2 due to its adsorption on the metal surface or on the film of the previously formed oxide.