South Pars gas field is the largest gas field in the world and is shared between Iran and Qatar.One of the most important projects in this field is the development of Phases 17 and 18. This mega project is one of the most important projects implemented in the South Pars gas field.This paper examines the impact of domestic inflation on the costs of implementing these phases over a period of ten years(2003-2013) .The main purpose of this study is to calculate and compare the costs of implementing this project under non-inflationary conditions.For this purpose, the main and standard activities of this phases is selected and its costs calculated and then neutralize inflation indicators for the desired time period to be compared between inflation and non-inflationary states.Wilcoxon test used to compare two dependent groups.Based on statistical analysis,assuming the absence of other factors,the expenditures of selected activities in phases 17and 18 of South Pars in the inflationary state were significantly higher than the non-inflationary state Keywords:South Pars Gas Field, Domestic Inflation