Foreign trade surpassed pre-crisis levels in 2005 and continues to expand. North Korea has a number of special economic zones (SEZs) and Special Administrative Regions where foreign companies can operate with tax and tariff incentives while North Korean establishments gain access to improved technology. Initially four such zones existed, but they yielded little overall success. The SEZ system was overhauled in 2013 when 14 new zones were opened and the Rason Special Economic Zone was reformed as a joint Chinese-North Korean project. The Kaesong Industrial Region is a special economic zone where more than 100 South Korean companies employ some 52,000 North Korean workers. , China is the biggest trading partner of North Korea outside inter-Korean trade, accounting for more than 84% of the total external trade ($5.3 billion) followed by India at 3.3% share ($205 million). In 2014, Russia wrote off 90% of North Korea's debt and the two countries agreed to conduct all transactions in rubles. Overall, external trade in 2013 reached a total of $7.3 billion (the highest amount since 1990), while inter-Korean trade dropped to an eight-year low of $1.1 billion.