The gas typically used to fill the tubes of vehicle tires is nitrogen (N2). Nitrogen is favored over compressed air because it is less likely to escape through the tire's rubber due to its larger molecular size. In addition, nitrogen has a more stable pressure than air, which reduces the risk of tires losing pressure and helps maintain proper tire pressure for longer periods of time. This can improve fuel efficiency, extend tire life, and enhance vehicle handling and safety. While nitrogen is the most common gas used in tires, compressed air can also be used to fill tires, although the benefits of using nitrogen may not apply in this case.