Approximately 90% of the discovered fields in Iran are in carbonate reservoirs making this country as one of the largest carbonate producers in the world. Iranian depleted zones are increasing, as most of the fields become mature. High pressure drop in most of these fields such as Parsi, Karanj, Aghajari, Gachsaran, Bibi Hakimeh, Lab Sefid, Dehloran, Danan and Mal Kouh caused several drilling and production problems. The current condition for new operation challenges in Iranian oilfields emphasizes the significance of utilizing new tools and methods. Implementing underbalanced drilling (UBD) technology in Parsi oilfield, located in south western part of Iran, may offer a solution to the challenges of operations of the field. Parsi has undergone substantial pressure loss over its history of nearly 50 years, and it is characterized by the highly fractured, vuggy Asmari formation. That combination of a challenging reservoir and low pressure has led to increasing problems for traditional overbalanced approaches. Many papers have been published discussing potential UBD advantages for southern Iranian oilfields; however, few papers are available about the challenges of this technology. Despite the increasing experience in this field, the value of UBD has not been fully acknowledged. This paper investigates the main UBD challenges in Parsi oilfield and summarizes the solutions to deal with them.