When getting ready to buy a new vechicle-noticed an add-on sticker"Nitrogen in all (4) tires" price was $199.00-no kidding! I decided to look into this since we use nitrogen to test industrail a/c equipment for freon leaks-(because it is cheap!). I Googled 15" tire x 9" volume of air =4.8 cu.ft @ 30 psi. lets say 5cu.ft-for (1) tire. a 300cu.ft bottle of nitrogen costs $29.00 includes bottle rent. Ok simple math (1) 300cu ft bottle will fill 60 tires. Thats $ 2.00 per tire. However you also get these cheesy bright green valve stem caps-maybe that is the Extra $$$, hah-watch out! To boot when the weather gets cold the nitrogen contracts even more than compressed air-so I am not seeing any advantages. BTW the air we breath is like 78% nitrogen, some Oxygen, Co2, traces of other.Buyer beware!