I know that when converting any 2-stoke to run straight alcolhol, the carb has to be modded or replaced so that a LOT more fuel is delivered to the engine. Ignoring the seal deterioration and water absorption problems, I don't see why it should be a problem running E15-20 in a chainsaw as long as it's properly tuned for it. There in lies the problem though. The saw comes from the factory tuned to run lean already on E10 to satisfy the EPA. Then Joe Shmoe operator puts in E15-20 and the already lean running saw runs even leaner. In some cases, lean enough to seize the saw. For those of us that pay close attention to the tune of our saws and tune them regularly, I don't see it being a problem. We might even get a slight performance advantage out of it. Storability becomes our biggest problem, with the resulting possible seal damage and water absorption. This is likely compounded by the fact that most fuel tanks are plastic instead of metal.