The MS 391 features our newest engine technology that adds fuel efficiency while reducing emissions as compared to other models. So, when you're starting a big job, you'll be confident that your chainsaw will get the job done without needing to refuel very often. In addition, you can rest assured knowing that your chainsaw won't hurt the environment. This chainsaw also features an optimal power-to-weight ratio. This chainsaw is cut out for the big jobs in fields, farms, and ranches. Lastly, the MS 391 features a 20-inch bar length that's big enough for tough jobs but small enough for you to use for long periods of time.