UPS, a shipping company that relies heavily on its boxy brown trucks, says it plans to buy up to 46 million gallons of renewable diesel fuel during the next three years in an effort to replace 12 percent of the fossil fuels. The company, which announced the initiative on July 29, says the fuels it plans to procure from three producers are made from several organic-based sources, including animal fats and other waste oils, including palm oil. They also are virtually chemical twins of oil-based diesel and so can be used interchangeably with them both in pipeline and in engines.