Ultra-low-sulfur diesel (ULSD) is diesel fuel with substantially lowered sulfur content. Since 2006, almost all of the petroleum-based diesel fuel available in Europe and North America has been of a ULSD type. The move to lower sulfur content allows for the application of advanced emissions control technologies that substantially lower the harmful emissions from diesel combustion. Testing by engine manufacturers and regulatory bodies have found the use of emissions control devices in conjunction with ULSD can reduce the exhaust output of ozone precursors and particulate matter to near-zero levels. In 1993 the European Union began mandating the reduction of diesel sulfur content and implementing modern ULSD specifications in 1999. The United States started phasing in ULSD requirements for highway vehicles in 2006, with implementation for off-highway applications, such as locomotive and marine fuel, beginning in 2007.