This communication reports the effects of multiphase flow on the corrosion product formed on the surface of 1018 C-steel coupons in oil and gas lines in presence of inhibitor oleic imidazoline. Both bulk and surface analytical techniques reveal the presence of FeCO3, a classic example of CO2 corrosion. While significant changes in the surface morphology with flow condition are monitored by SEM and OM, detailed AES and XPS analysis show the deterioration of inhibitor chemistry as the flow is increased from full pipe (Fr = 0) to slug flow (Fr = 6). XPS shakeup satellite lines in the N (1s) spectra have been useful in the analysis. (C) 2000 Elsevier Science Ltd. All rights reserved. This communication reports the effects of multiphase flow on the corrosion product formed on the surface of 1018 C-steel coupons in oil and gas lines in presence of inhibitor oleic imidazoline. Both bulk and surface analytical techniques reveal the presence of FeCO3, a classic example of CO2 corrosion. While significant changes in the surface morphology with flow condition are monitored by SEM and OM, detailed AES and XPS analysis show the deterioration of inhibitor chemistry as the flow is increased from full pipe (Fr = 0) to slug flow (Fr = 6). XPS shakeup satellite lines in the N (1s) spectra have been useful in the analysis.