The sale will help RWE to shore up its finances after it reported its first net loss in more than 60 years earlier this month.
The deal will see the Letter One group, set up by Russia’s fourth-richest man Mikhail Fridman and co-investor German Khan last year, take control of the company and responsibility for €0.6 billion of debt.
The sale must still be approved by RWE’s supervisory board and regulators in several countries, RWE said, and the deal is expected to be closed later in the year.
In April last year, RWE chief executive Peter Terium said DEA, which pumps oil and gas in the UK, Germany and Norway, was “no longer” of strategic importance.
In a statement, Terium said: “This agreement is a major milestone in delivering our announced strategic realignment of the group.
“In addition, it is a further and essential step towards improving our financial strength.”