Per the manufacturer, the Husqvarna 455 Rancher operates best with non-ethanol gasoline, 89 octane or higher, mixed with 2-stroke oil at a ratio of 50:1. This is about 2.6oz of oil per gallon of gasoline. While less than ideal, you may use ethanol-containing fuel that is no more than 10% ethanol, but any greater percentage will void your warranty. Ethanol-containing fuel is not good for small engines generally, as it is hygroscopic and will pull water from the atmosphere into the mixture and possibly damage the engine. Here are a selection of 2 stroke oils that will work for your Husqvarna 455 Rancher chainsaw.