Well, yes and no. No, they don't give it a line item and its not an official fee. But yes you pay for it, its incorporated in the price of the fare which is usually higher (unless a major is matching a F9/NK fare), so your paying for it regardless. If you wish not to have to even think about what fees apply then you are welcome to pay the higher fare on the traditional carrier, but I am willing to put in the effort of knowing that they will have a seat fee, a carry-on fee, etc. My major complaint with F9 these days are the seats. I haven't personally sat in the seats but my brother was on a 3 1/2 hour flight and was disappointed in them. I hoping that the stretch seating is better according to the Frontier video on the new seats, stretch has lumbar support and additional padding.

So If I'm saving money in the end, it doesn't really matter to me if they charge me a cabin oxygen fee. `