Photograph by Ned Therrien/Getty Images
"Black liquor," a byproduct of the wood pulping process, has been used by paper companies to power mills for decades. In 2007, a change to a law promoting the use of alternative fuel inadvertently entitled paper companies to a 50c per gallon tax credit for using black liquor. International Paper Co. reported a 93 percent increase to 2009 first-quarter net income, thanks to a $540 million black liquor credit. The potential value of credits if allowed to remain in force was estimated to be as high as $25 billion. Although Congress closed the loophole in 2010, paper companies were allowed to keep their windfalls for prior years.