US$958 billion, creating a trade deficit of US$222 million. The deficit increased again in 2005, to US$339 million, mainly because cotton exports decreased and domestic demand for goods increased. In 2005, the current account deficit was US$86 million, having shown a general downward trend since the late 1990s. The estimated current account deficit for both 2006 and 2007 is 4.5% of GDP, or about US$90 million in 2006. In 2005 the overall balance of payments was US$14 million. The estimated overall balance of payments for 2006 is US$8 million. At the end of 2006, Tajikistan's external debt was estimated at US$830 million, most of which was long-term international debt. This amount grew steadily through the 1990s and early 2000s because of state borrowing policy. In 2004 Tajikistan eliminated about 20% of its external debt by exchanging debt to Russia for Russian ownership of the Nurek space tracking station, and by 2006, rescheduling negotiations had reduced the debt by about two-thirds as a percentage of gross domestic product. In the early 2000s, foreign direct investment has remained low because of political and economic instability, corruption, the poor domestic financial system, and Tajikistan's geographic isolation. The establishment of businesses nearly always requires bribing officials and often encounters resistance from entrepreneurs with government connections. To attract foreign investment and technology, Tajikistan has offered to establish free economic zones in which firms receive advantages on taxes, fees, and customs. In 2004, the parliament passed a law on free economic zones and in 2008 passed a decree creating two zones: the Panj Free Economic Zone and the Sughd Free Economic Zone. In 2003 foreign direct investment totaled US$41 million; it increased to US$272 million in 2004 because of the debt-reduction transaction with Russia. In the first half of 2005, the figure was US$16 million. Beginning in 2005, the Russian Rusal aluminium company resumed operations to complete the hydroelectric station at Rogun on the Vakhsh River and expand aluminum production at the Tursunzade plant. That plant was scheduled for possible sale to Rusal in 2007. Also in 2005, Russia and Iran resumed work on the Vakhsh River Sangtuda hydroelectric project. Gazprom, the Russian natural gas monopoly, allocated US$12 million for oil and gas exploration in Tajikistan in 2007 after spending US$7 million in 2006. In 2005 the Russian telecommunications company VimpelCom bought a controlling share of Tajikistan's Tacom mobile telephone company. As of 2006, Turkey tentatively