Countries engaging in international trade, maintain reserves to ensure no interruption. A rule usually followed by central banks is to hold in reserve at least three months of imports. Also, an increase in reserves occurred when commercial openness increased (part of the process known as globalization). Reserve accumulation was faster than that which would be explained by trade, since the ratio has increased to several months of imports. Furthermore, the ratio of reserves to foreign trade is closely watched by credit risk agencies in months of imports.