Yes, it is possible to use 91-octane gasoline in a motorcycle, as long as the manufacturer's recommendations permit it. Many motorcycles are designed to run on unleaded gasoline with an octane rating of 87 or higher. However, it's essential to refer to the owner's manual or contact the motorcycle manufacturer to determine the recommended octane rating for your specific model. Following the manufacturer's guidelines will ensure optimal performance and prevent any potential damage to the engine.