I. S outhern A frican C ustoms U nion R evenue S urge and F iscal R esponse in B otswana , L esotho , N amibia, and S waziland 1 A. Introduction 1. The Southern African Customs Union (SACU), the oldest customs union in the world, comprises Botswana, Lesotho, Namibia, and Swaziland (known as the BLNS countries) and South Africa . The increase in annual average SACU revenue collected by BLNS countries from about 12.7 percent of GDP in the early 2000s to 20.7 percent in 2008 has had major macroeconomic and fiscal implications. The revenue surge