The black liquor tax credit, once part of the alternative fuel credit, was a tax loophole allowed to companies for using black liquor - a paper production byproduct that the paper and pulp companies were already using - mixed with diesel as a fuel source. The paper and pulp companies began adding diesel to their black liquor so they could claim a tax credit. This achieved the reverse of what the bill intended, increasing the use of fossil fuels and reducing the use of biofuels.