The retail market may be running out of gas but Sydney has its first permanent stand-alone oxygen bar.

The O2 Bar, which opened at Darling Harbour's Harbourside yesterday, offers 90 per cent-pure flavoured oxygen for $1 a minute for up to 15 minutes, owner Alexi Fahad said.

Flyers for the new bar claim oxygen can increase energy, ease hangover headaches and stress, and help combat jet lag.

But experts say there are no known benefits for healthy people in breathing pure oxygen, and too much may not be good for you.