It's been about two months, so it was about time to fill the fuel tank in the Volkswagen. The weather having been plenty warm here lately, I figured that Wacker Oil out in Manchester would have some B100 biodiesel for sale. When I got there, though, they only had B50 and B99--50% and 99% biodiesel, respectively. The reason for this is that the state of Michigan implemented a tax credit for biodiesel blends (the credit goes to the blender, not the end consumer except in the price). The credit is a penny per gallon for each percentage point of biodiesel. So B50 has a 50 cent per gallon credit, and B99 has a 99 cent per gallon credit. They don't sell 100% biodiesel anymore, though, because that's not a "blend."