Allen & Overy is advising one of its oldest clients on its final deal as lubricants company Burmah Castrol sells up to global giant BP Amoco.
The firm has acted for Burmah Castrol since the 1960s, and corporate partner Richard Rowland has worked for it since taking partnership in 1974.
BP Amoco has agreed to buy the company for £3bn in a deal that was rushed through in a matter of days.
Law firms on both sides of the Atlantic have been left with the task of getting regulatory approval.
Linklaters & Alliance is representing BP Amoco in the buyout, with US law firm Sullivan & Cromwell working on obtaining US clearance from the Federal Trade Commission.
Burmah Castrol is instructing Simpson Thach-er & Bartlett for its US work.
Rowland says: "The time necessary to get regulatory approval means that it does not fit with a bid timetable, so offers are being made preconditional on getting approval.
"We will be working heavily with the other firms for the next few months providing the necessary information about Burmah Castrol."
Rowland is leading the Allen & Overy team of seven. The six-strong team at Linklaters is being led by corporate partner Lee Taylor with competition partner Michael Cutting and tax partner Conor Hurley.