LONDON - OPEC producer Kuwait's oil reserves are only half those officially stated, according to internal Kuwaiti records seen by industry newsletter Petroleum Intelligence Weekly (PIW).

"PIW learns from sources that Kuwait's actual oil reserves, which are officially stated at around 99 billion barrels, or close to 10 percent of the global total, are a good deal lower, according to internal Kuwaiti records," the weekly PIW reported on Friday.

It said that according to data circulated in Kuwait Oil Co (KOC), the upstream arm of state Kuwait Petroleum Corp, Kuwait's remaining proven and non-proven oil reserves are about 48 billion barrels.

Officials from KOC were not immediately available for comment to Reuters.

PIW said the official public Kuwaiti figures do not distinguish between proven, probable and possible reserves.

But it said the data it had seen show that of the current remaining 48 billion barrels of proven and non-proven reserves, only about 24 billion barrels are so far fully proven -- 15 billion in its biggest oilfield Burgan.

Kuwait has been adding up to 500 million barrels a year at Burgan which means the remaining non-proven reserves of some 5.3 billion barrels will likely be upgraded to proven, according to PIW.

Three consortia led by BP, Chevron and ExxonMobil are in the race for Project Kuwait, a 20-year operating service contract to raise crude capacity at four oilfields in the north of Kuwait.