Exports were the key to South Korea's industrial expansion. Until 1986 the value of imports was greater than exports. This situation was reversed, however, in 1986 when South Korea registered a favorable balance of trade of US$4.2 billion. By 1988 the favorable balance had grown to US$11.4 billion. Financing this persistent, although not unexpected, gap between domestic and imported resources was a principal concern for economic planners. In the 1950s and 1960s, much of the trade deficit was financed by foreign aid funds, but in the last two decades, borrowing from and investment in international capital markets have almost completely substituted for economic aid.