LONDON (Financial Times) — Kazakhstan’s giant Kashagan oil field will produce 25 percent more oil than expected once it hits peak production, international companies developing the field have found.

News that the field, the largest and most important discovered in more than 30 years, will yield significantly more than the 13 billion barrels forecast is a breakthrough as dwindling world oil supplies and problems accessing oil-rich countries such as Iraq raise doubts about meeting rapidly increasing demand.

The Financial Times has learnt that peak production of the Kashagan field in the Caspian Sea, due at the end of the next decade, is expected to be 1.5 million barrels a day, 25 percent higher than published estimates. The field, operated by Eni, Italy’s biggest oil and gas group, is expected to pump this amount each day for more than 10 years, meaning it will yield 10 percent more reserves than currently assumed.

Kashagan’s extra production is almost equivalent to all the oil produced in Sudan in 2005, according to latest figures. But the complicated field – originally due to start pumping oil in 2005 – will take longer to develop, Eni is expected to warn shortly. The operator has pushed back its start date several times, most recently to 2008, but is now set to announce production will not start until 2009 at the earliest.

The field will also cost its partners, which include some of the world’s biggest oil companies, more than the official estimate of $29 billion. It is now expected that the minimum price tag of Kashagan, already the world’s most expensive energy project, will be in the mid-$30 billion range.

The field’s partners include Total of France, Royal Dutch Shell, ExxonMobil and ConocoPhillips of the U.S., Inpex of Japan and KazMuneiGaz. Steamy summer conditions, winter temperatures of -40 degrees centigrade, a sensitive environment and high quantities of poisonous hydrogen sulfide make Kashagan perhaps the world’s most complicated field.

“The project has been delayed but, from an engineering point of view, we need to give them credit for moving forward. I really admire the challenges they are taking on,” said one analyst, who called the increased expectations “extremely important”.

Disputes among the partners have also slowed down the project. But the secondment of 50 engineers from ExxonMobil, the world’s biggest energy group, has eased tensions, people close to the project said.

Kashagan is the world’s most important oil field in terms of reducing reliance on Russia and the Organization of the Petroleum Exporting Countries, the cartel that controls 60 percent of the world’s remaining oil reserves, said Joseph Stanislaw, president of JAStanislaw Group, the advisory firm, and an expert on the region.

“Kashagan is part of the new energy geopolitics being driven by the U.S. The field is large and significant and pulls the center of gravity away from Russia and the Middle East,” he said.