The CBI may ask oil ministry to appoint an expert to assist it in understanding transactions surrounding Reliance Industries' crown jewel KG-D6 fields, where the company has shown a phenomenal increase in cost of producing gas.

The central bureau of investigation wants to understand the arguments offered by Mukesh Ambani's firm when it raised the cost of developing Dhirubhai 1 and 3 gas fields in the KG-D6 block from USD 2.39 billion proposed in 2004 to USD 5.196 billion in Phase-1 and another USD 3.3 billion in Phase-II.

Exploration and production of oil and gas from deep sea being complex issues, the agency wants to use the expertise of a domain expert to understand if all the expenses proposed by Reliance and approved by the directorate general of hydrocarbons (DGH) were justified.

Sources in the agency said that the CBI had approached an expert for making a detailed analysis who sought a fee of over Rs 20 lakh following which it decided to write to the petroleum ministry.

"We will be writing to the petroleum ministry for hiring the same expert for us as the agency cannot make such a huge payment," a senior CBI official said.

A preliminary enquiry into the case was registered in November 2009 on request of petroleum ministry following several objections raised by the anti-corruption watch dog -- CVC -- on the KG-D6 fields deal.

The central vigilance commission had forwarded a complaint in which it was alleged that there was a phenomenal increase in capital expenditure from USD 2.4 billion to about USD 8.8 billion in the project.