Introduction: Interpreting an arterial blood gas (ABG) is a crucial skill for physicians, anaesthetics, nurses, respiratory therapists, and other health care personnel. ABG interpretation is especially important in critically ill patients. The goal of present study is to compare the clinical utility of different methods of arterial blood gas analysis in critically ill patients with mixed complex acid base disorders. Material and methods: This study was conducted on 200 critically ill patients of 12 to 85 years age, admitted in ICU (medical and surgical) at Govt. medical college and attached M.B.S. Hospitals Kota. All data were collected and studied by Linear regression and Bald and Altman analysis. Results: Six step approach allowed the detection of additional or different metabolic acid–base alteration in 57.50 % of critically ill patients; and the inclusion of albumin corrected anion gap in the six step analysis based on change in anion gap due to change in serum concentration of albumin in critically ill patients resulted in an 21% more additional or different diagnosis as compared to six step approach.