An oil tanker has started loading a cargo of condensate, or ultra-light oil, the first such export from the United States since the easing of a 40-year-old ban on U.S. crude exports, two sources familiar with the matter said on Wednesday. Westport Petroleum Inc, the Franklin, Tennessee-based shipping arm of Japanese trader Mitsui & Co, chartered the BW Zambesi, an LR1 tanker, also known as a Panamax class vessel, in mid-July for the voyage. The tanker, owned by BW Group, docked at the Galveston terminal in Texas on Tuesday, AIS data on Reuters showed. It will load just over 400,000 barrels of condensate and is expected to arrive in Asia in early September, one source said. South Korean refiner GS Caltex has bought the cargo from Mitsui.