MOSCOW - Russian gas export monopoly Gazprom may lose around 380 billion roubles ($13.17 billion) in 2009-2010 due to higher than expected custom duties, Vedomosti business paper reported on Tuesday.

The state-run gas giant has already asked the government to settle the dispute that could cost the company around 111.7 billion roubles this year and 274.4 billion roubles in 2010, the paper cited two sources close to Gazprom as saying.

But it is still unclear if the final decision will be made in favour of Gazprom or the Federal Custom Service.

The conflict has emerged after the Custom Service changed the method by which Gazprom should register payments for custom declarations.

Gazprom was obliged to declare the preliminary volume of the supplied gas on Russia's border, which as a rule exceeded the volume the company finally sells to its customers.

One of the sources told the paper the situation had spiralled out of control as Gazprom continued to pay the custom duties on the basis of the volume of the gas it supplied to its clients, while the Custom Service calculated duties and fees based on preliminary declarations.

Gazprom may cut its investment programme for 2010 should it pay additional duties, the sources said. ($1=28.85 Rouble) (Reporting by Dmitry Sergeyev; Editing by Lincoln Feast)