Russia’s tax authorities have claimed $256 million in back taxes on TNK-BP, and the Natural Resources Ministry has extended its investigation into the company by one month. TNK-BP’s co-owner has called on the Russian government to broaden tax breaks for the oil sector to prevent a decline in production. Shareholders of Sibur Management want to buy a controlling stake in Gazprom’s petrochemicals unit. Gazprom is poised to unseat General Electric Co. as the world’s fourth-largest company by market value. Lukoil and other buyers are in talks with Regal Petroleum about purchasing its gas fields in Ukraine “five months after a similar deal with Shell fell apart.” Norway’s $400 billion oil fund voted last year for tougher environmental standards at US oil giant Exxon Mobil than the Scandinavian nation imposes on its own oil major, StatoilHydro. Gas producer Novatek has signed a $800 million three-year syndicated loan.