A global anti-corruption and accountability watchdog group, Global Witness, has calculated that the OPL 245 deal deprived Nigeria of double its annual education and healthcare budget, the British Broadcasting Corporation reports on Monday.
The group has spent years investigating the deal, which gave Eni and Shell the rights to explore OPL 245, an offshore oil field in the Niger Delta.
It has commissioned new analysis of the way the contract was altered in favour of the energy companies and concluded Nigeria’s losses over the lifetime of the project could amount to $5.86bn, compared to terms in place before 2011.
The analysis was carried out by Resources for Development Consulting on behalf of Global Witness, as well as three non-governmental organisations, namely HEDA, RE:Common and The Corner. The estimated losses were calculated using an oil price of $70 a barrel as a basis.
Eni has criticised the way it was calculated because it ignored the possibility that Nigeria had the right to revise the deal to claim a 50 per cent share of the production revenues, according to the BBC report.
Eni and Shell were accused of knowing the money they paid to Nigeria would be used for bribes.
The Italian and Anglo-Dutch energy giants denied any wrongdoing.
The unfolding scandal, which is being played out in an Italian court, has involved former MI6 officers, the Federal Bureau of Investigation, a former President of Nigeria, as well as current and former senior executives at the two oil companies.
The former Nigerian oil minister, Dan Etete, was found guilty by a court in France of money laundering and it emerged he used illicit funds to buy a speed boat and a chateau.
Campaigners said the deal should be cancelled.
“We discovered that Shell had constructed a deal that cut Nigeria out of their share of profit oil from the block,” Ava Lee, a campaigner at Global Witness, told the BBC’s World Business Report.
“This amount of money would be enough to educate six million teachers in Nigeria. It really can’t be underestimated just how big a deal this could be for a country that right now has the highest rates of extreme poverty in the world.”
The court in Milan is weighing evidence of how Etete awarded ownership of OPL 245, which is estimated to contain nine billion barrels of oil, to Malabu, a company he secretly controlled.
He is accused of paying bribes to others in the government, such as former President Goodluck Jonathan, to ensure that the process went smoothly.