A year after Eni announced the largest discovery in its exploration history, a giant gas find in Mozambique, rival oil companies are falling over each other to get a piece of the action.

"It was clear from the start it was a major discovery that changed the ball game," a source close to the Milan-based company told Reuters.

And the find is getting bigger by the day, drawing interest from some of the world's largest energy players, many of which are coming late to the party in the world's most prolific area for new discoveries.

"Eni is in early talks with a few large players like Shell and Exxon, and, interestingly, a few large LNG buyers that could cover production and help speed final investment decisions," a source familiar with the matter said.

The Maputo government says the Rovuma field, home to the prospects discovered by Eni and Houston-based Anadarko off Mozambique's northern coast, boasts an estimated 150 trillion cubic feet (tcf) of gas.

Energy consultancy Wood Mackenzie classifies it as one of the world's biggest three gas basins.

The giant gas fields have showcased a part of the world some are calling the new Middle East. The pickings are so rich that East Africa's "new frontier" is now expanding north past Tanzania to Kenya, Ethiopia and even war-ravaged Somalia.

But it's Mozambique that has captured the imagination. Its deep waters are already peppered with rigs, and shiny new liquefied natural gas (LNG) plants will soon dot the coast to feed gas-starved Asian markets.

Four of the five largest oil and gas discoveries in the world this year have been made off Mozambique, including three by Eni, according to Wood Mackenzie.

"We reckon Eni and Anadarko are sitting on 85 tcf of recoverable gas, enough for multiple LNG trains, and we're probably only at the half-way stage," says Martin Kelly, head of the consultant's Sub-Sahara Upstream Research team.

The two LNG trains scheduled to be built in a first phase will liquefy 10 million tons per year, enough to meet almost 10% of gas demand in Japan, one of the biggest Asian markets.

"There's going to be a lot of competition and jostling for position and Eni with its size and experience could be a kingpin," says Kelly.

Wake-up call

Most of the world's big energy players have been late in waking up to East Africa and are now faced with the choice of either splashing out on new concessions or buying into operations that gambled on big finds.

France's Total, a deepwater specialist, recently bought into a Rovuma venture led by Malaysia's Petronas, while Shell lost out to Thailand's PTT in a $1.9 billion bid for Cove Energy, a partner of Anadarko in Mozambique.

"I remember this used to be a counter-consensus exploration play until the big finds came in last year. Just goes to show you can have all the right skills and a big budget and still miss the train," Bernstein energy analyst Rob West said.

Eni, Africa's biggest foreign operator, has 70% of the Mamba field it operates with Galp Energia, Korea's KOGAS and Mozambique's state-owned ENH in the Rovuma basin.

The field lies close to the Prosperidade acreage operated by Anadarko and junior partner Cove.

Both operators insist they won't know how much gas they've got until appraisal is complete next year. But already they are gearing up to sell down stakes to fund big investment plans and limit country risk in one of the poorest parts of the world.

Eni, which sees a long-term need for 10-12 LNG trains, has slapped a ballpark number on investments of around $50 billion.

Anadarko, with no LNG credentials of its own, is looking to sell a third of its 36.5% stake, while Eni is expected to sell off at least 20% of its holding for cash or assets.

"One option Eni is playing with is the idea of creating two sub-blocks - selling a majority stake in one and keeping a majority in the other," a source close to the situation said.

Milan broker Mediobanca says that, based on the Cove deal, Eni's 70% stake in Mamba field is worth $17.2 billion.

China supply chain

Mozambique's remoteness and lack of infrastructure means heavy spending will be needed on roads, railways and ports even before the new and expensive LNG terminals are built to liquefy the first gas expected in 2018-2019.

Finding skilled workforce will also be a challenge.

"If I were Eni I'd be looking at the emerging national oil companies. The Chinese can provide a supply chain and help boost returns," Banco Santander oil analyst Jason Kenney said.

Former BP head Tony Haywood has said a key benefit of his group's teaming up with China's CNPC in Iraq was access to the Chinese supply chain. China can deliver just about anything cheaper than elsewhere and not just rigs.

Together with India, Beijing is targeting Africa for natural resources to fuel its economy, and bypassing the volatile Middle East for energy supplies is particularly appealing.

Yet one banana skin for Eni could be what in the industry is known as "unitisation".

A lot of the gas discovered is thought to be one enormous field straddling the prospects of Eni and Anadarko. Eni has said a third of its 75 tcf of gas is exclusively within its block, while the rest is in a communicating area.

What that means is the two will have to sit down with the Maputo government to decide who is in charge and agree a plan to bring the gas to shore and build LNG plants and infrastructure.

"The challenge is that all of these projects have a lot of participants, and just coordinating between the operators and the participants within one consortium is probably quite a challenge," said Anne Fruhauf, director for Africa energy at consulting firm Horizon Client Access.

Talks are already under way, and while Eni and Anadarko claim relations are good, some are concerned the spoils at stake could create trouble.

"I've heard that Eni wasn't keen on working with Anadarko at all," one industry source said.