Oil producer ConocoPhillips and Tyson Foods, the world's largest meat producer, are collaborating to produce and market diesel fuel for U.S. vehicles using beef, pork and poultry fat, The Associated Press reports. ConocoPhillips plans to spend about $100 million over several years to produce the fuel, Chairman and Chief Executive Jim Mulva said at a news conference. It hopes to introduce the fuel at gas stations in the U.S. Midwest in the fourth quarter of this year. But some renewable-fuel advocates say ConocoPhillips will be able to take unfair advantage of a tax credit designed to create new refining capacity for clean-burning fuels, even though they'll be using existing refineries. The companies expect to increase production over the next couple of years to as much as 175 million gallons a year, or about 3 percent of ConocoPhillips' total U.S. diesel production, AP reports.