On 16 April 2009 the State of California introduced fuel use regulations (“the Vessel Fuel Rules”) the purpose of which was to reduce air pollutants affecting the state of California by requiring ocean-going vessels to use cleaner marine fuels. The Vessel Fuel Rules applied to vessels operating within 24 nautical miles off the California coastline, an area encompassing 14,000 square miles of ocean beyond the three-mile coastal zone. They only covered vessels calling at a California port, and there was an exemption for vessels simply travelling through the region. The regulations were to take effect on 1 July 2009.