Objectives: Arterial blood gas (ABG) analysis is an essential investigation for assessment of ventilation, oxygenation and acid–base status in critically ill patients. Arterial puncture to obtain arterial blood is more invasive procedure than venous and has more potential complications. The present study was undertaken to find out the correlation between arterial and peripheral venous blood gas (VBG) values for PO2 (Partial pressure of oxygen), PCO2 (Partial pressure of carbon dioxide), pH (Potential of hydrogen) and HCO3 (bicarbonates). Material and Methods: A total of 131 consecutive patients admitted to intensive care unit (ICU) requiring ABG analysis to determine their acid–base status or ventilatory status were included in the study. Arterial and venous blood samples were obtained with a heparinised syringe within <15 min, after performing modified Allen’s test and were analysed using blood gas analysis machine. The mean of pH, pCO2, HCO3, and PO2, values in arterial and venous samples was determined, along with peripheral arterial oxygen saturation (SpO2) of patients. Results: ABG and VBG analysis correlated well for pH, pCO2 and HCO3, as their correlation coefficient (r) were 0.976, 0.992 and 0.984, respectively, whereas PO2 has correlation coefficient of 0.010 which suggests that there was poor correlation in PO2. For each unit increase in pCO2, pH and HCO3 of VBG, all these ABG changes by 0.9831 units, 0.914 units and 0.992 units, respectively. Peripheral O2 saturation (SpO2) correlates well with arterial O2 saturation, however, does not correlate with venous O2 saturation. Conclusion: The results show that VBG analysis can be a substitute for ABG for evaluation of ventilatory function and acid–base imbalance for pH, pCO2 and HCO3 in patients of ICU setup in many clinical contexts.