Mayer Brown and Stephenson Harwood have taken roles on the largest flotation of an oil and gas company on the London Stock Exchange – by finances raised – in the last five years.

The complex deal, which took almost two years to complete, saw Eland Oil and Gas raise £118m on its Alternative Investment Market listing, enabling the company, in a joint venture with Starcrest Nigeria Energy, to acquire a 45% stake in the onshore Niger delta oilfield Oil Mining Lease 40 (OML 40) for $154m (£97m).

Mayer Brown acted for Canaccord Genuity in connection with its role as nominated adviser and broker to Eland Oil & Gas with a team led by corporate and securities partners Robert Hamill and Kate Ball-Dodd.

Meanwhile, a Stephenson Harwood team led by corporate partner Tony Edwards and energy partner Jeremy Sheldon advised Eland on the initial public offering (IPO) and its joint acquisition of OML 40.

The firm, which advised on aspects of corporate finance, energy, banking, regulatory and incentives, also referred the international aspects of the deal to seven other firms: Nigeria's Streamsowers & Kohn, Covington & Burling in the US, Norton Rose, BLC Chambers in Mauritius, offshore firm Ogier, Switzerland's Baer & Karrer, Dillon Eustace in Ireland and Australia's Minter Ellison.

Hamill (pictured) said the deal had been "a highly complex process", but suggested it could be seen as "a sign of how regulatory change in Nigeria is affecting the oil industry as the government looks to boost local participation".

"The thing is we all know that current markets are being very difficult, so it is quite a feat to get an IPO of that size away," said Edwards. "When you are doing a deal involving a huge counter-party and a culture with a set way of doing things, that doesn't entirely lend itself to completing an acquisition in tandem with the listing."

"It was challenging because things run at a different pace," acknowledged Sheldon. "There is a backdrop of political considerations, so from that point of view it was hard, but these are not insurmountable challenges."