ABUJA Nigeria's lower house opened an investigation on Tuesday into an offshore oil field owned by Royal Dutch Shell (RDSa.L) and Eni (ENI.MI), the latest inquiry into their acquisition of the OPL 245 licence block which could hold up to 9.23 billion barrels of oil, according to industry figures.
Earlier this year the Dutch and Italian authorities launched their own investigations.
The acquisition in 2011 was a "breach of due process that resulted in monumental revenue loss to the country," said Yakubu Dogara, speaker of Nigeria's House of Representatives.
A spokesman for Shell said: "As this matter is the subject of current investigations, it would be inappropriate for us to comment."
The licence was initially awarded in 1998 by former Nigerian oil minister Dan Etete to Malabu Oil and Gas, a company in which he was a shareholder.
It was then sold for $1.3 billion in 2011 to Eni and Shell. According to documents from a British court, Malabu received $1.09 billion from the sale, while the rest went to the Nigerian government.
In 2014 a Milan court placed Eni under investigation over the purchase and the probe was later widened to Shell.
(Reporting by Camillus Eboh; Writing by Paul Carsten; Editing by Greg Mahlich/Ruth Pitchford)