Kazakh Deputy Finance Minister Daulet Yergozhin said lawyers utilized ambiguities in contracts for the BP-Eni consortium KPO to impose duties in the past and were looking at similar measures for the Tengiz field, The Financial Times reported.

"Lawyers are examining the contract. If they say we cannot legally impose the export tax, I will hand the oil group a letter exempting them from the tax," he said.

Kazakhstan imposed an export duty of $109.81 per metric ton, or about 7 barrels of crude, in July. Astana, the capital, had issued an exemption in May, however, citing protections outlined in contracts signed in the 1990s.

Oil officials said, however, they "strongly" believe they are still exempt from the export duties outlined in the contracts.

Energy analysts say Kazakhstan is facing economic uncertainty due to the fallout from the U.S. financial crisis, though Kazakh officials say that allegation is unfounded.