The gas most commonly used to inflate tires is nitrogen. Nitrogen is preferred in many situations due to its stable properties; it's non-flammable, less reactive, and has a lower permeability rate compared to oxygen. This means that nitrogen-filled tires maintain their pressure longer, which can improve fuel efficiency and tire lifespan. Additionally, nitrogen is less likely to cause tire deterioration and improve safety by reducing the risk of blowouts. Some automotive enthusiasts and professionals opt for nitrogen inflation in performance vehicles or racing tires, benefiting from its stability under varying temperature conditions.