Kazakhstan announced on Tuesday that it had initiated international arbitration proceedings against major oil companies, including Exxon Mobil, Chevron and Shell, regarding the deduction of $16.5 billion from the proceeds of two oil fields.

The official news agency quoted Energy Minister Almasadam Satkaliyev as saying that the government "has started an international arbitration against the companies operating the Karachaganak and Kashagan fields," adding that "the sums are 3.5 billion and 13 billion dollars."

The vast Kashagan field in the northern Caspian Sea is managed by the North Caspian Operating Company consortium, which includes Mazmuanegas, Eni, ExxonMobil, Royal Dutch Shell, Total Energy, China National Petroleum Corporation and Inpex.

The Karachaganak field in western Kazakhstan is operated by Eni, Shell and Kazmonaygas, along with Chevron and Lukoil.

The operating companies deducted some costs from the revenues of the two fields before sharing them with the government under production-sharing contracts.