you can safely use up to B20 (20% bio). Yes, it does offer slightly less power, and thus possibly slightly less mpg, but not much. Research the brand you get or ask them about quality, but using will generally keep your engine cleaner... which is why others say to stock up on oil filters. This is only required when switching a high mileage engine (with deposits) to biofuel (which cleans deposits out). If your engine is new-ish, you most likely will not have many buildups and you can keep your engine deposit free using bio blends. Also, most research shows engines longevity is extended by running bio.