Although the terms of the agreement have not yet been finalised, it is understood Montagu has won an "exclusive" right to buy a 39.5 per cent stake in RBG held by 3i. The Aberdeen firm is currently owned by 3i and Ashley Group, both of whom hold a 50 per cent share of the company's equity.
The group was formed in 2004 following the merger of three firms - Rigblast, Macgregor Energy Services and Mach-Ten Offshore. The deal was led by Rigblast founder John Ray, who is still chairman of RBG which employs some 4,500 worldwide.
3i has sold companies worth more than 1.7 billion this year as it continues attempts to lower its debt. In a half-year update last week, the private equity outfit said it had "transformed its balance sheet". Net debt had fallen to 352m from 854m in the same period last year - from a high of 2bn last year which sparked a credit rating downgrade. Its interim figures also showed that the value of its oil, gas and power portfolio had fallen to 61m from 98m the previous year.
RBG said yesterday: "RBG can confirm that it is in discussions regarding the future funding of the business. Given the sensitive nature of these discussions, we are unable to release further information at this time."
A spokeswoman for 3i declined to comment.