Boeing 747-8F Lands at Paris after First-Ever Transatlantic Biofuel Flight Sure, biofuel was only 15% of the fuel mixture, and biofuel also takes a lot of energy to produce, BUT this test is a good start and proves that this method is viable. My questions: Is this 15% biofuel mixture better than 100% fossil fuels? If so, how much better? Why "15%" ? Is that the maximum fuel blend of biofuel that will still allow the engines to run, based on experimentation, or is that an arbitrary/economic number?