Burren turned to Travers, while Freshfields advised Eni. The deal gives Eni access to Turkmenistan's lucrative oil and gas fields.
Burren's board rebuffed Eni's initial approaches of £10.50 and then £12 a share, as well as others from unnamed parties. The Korean National Oil Company may yet mount a rival bid, however.
At Travers, corporate partner David Innes led the team advising Burren.
The Freshfields team was led by head of energy Jonathan Rees and corporate partners Mark Rawlinson and Stephen Hewes. Financial adviser to Eni was NM Rothschild.
Rees advised Gazprom on its strategic alliance with Eni last year. Although the magic circle firm has a historic relationship with Eni UK, the company's Italian parent usually uses Slaughter and May's Italian best friend Bonelli Erede Pappalardo.
Burren is a longstanding client of Travers, with the firm advising the company on its 2003 flotation.
But Burren does instruct other firms: in May it turned to Ashurst for advice on the £77.83m purchase of a 5.5 per cent stake in the M'Boundi oilfield in the Democratic Republic of the Congo, a project on which it is a partner of Eni.
On that deal, Eni did not use outside counsel but turned instead to assistant general counsel for West Africa and the Far East Valentina Ferri (The Lawyer, 14 May).