With record-setting gas prices, a company called N2Revolution is selling the idea of nitrogen-filled tires for better fuel economy. Regular air, a mix of mostly nitrogen and oxygen, is more reactive to temperature fluctuations than pure nitrogen, so tires contract and expand more frequently. This increases tire wear and makes for less time spent at optimum psi, which affects fuel economy. Also, the oxygen in regular air oxidizes the rubber from within, causing more wear. Nitrogen, which is used in aircraft and race car tires, doesn't oxidize the rubber and stays at optimal psi under regular operating temperatures. N2Revolution claims that nitrogen doesn't dissipate through rubber as quickly, making the necessity of reinflation less frequent. Wikipedia disputes that claim, saying that nitrogen molecules are smaller than the combination of oxygen and nitrogen found in air, and smaller molecules will diffuse through rubber more quickly. The EPA (PDF) says that nitrogen-filled tires should cause about 3 percent better fuel economy. A dealer locator on the N2Revolution Web site shows where you can find its PurigeN98 nitrogen inflation system, but fill-up spots are few and far between, so far. On the West Coast, there are only four: one in Seattle and three around Los Angeles. Also, with per-tire fill-ups running up to $10, the cost effectiveness is debatable.