Oxygen. It makes up 21 percent of the air we breathe. It’s one of the earth’s most abundant elements. It’s free. But when it’s condensed, purified, and flavored, a five minute session of oxygen will set you back $5.

Two New Haven nightclubs, Alchemy and Lounge 215, have opened Connecticut’s first oxygen bars. The bars, both called CL02UD9, generate 96 percent pure oxygen and filter out nitrogen, argon and other impurities.

The oxygen is then mixed with flavors such as vanilla, orange and cranberry. Depending on the length of the session, the cost can range from $5 to $16. Despite the odd feeling of having to pay for something provided free of charge by nature, CL02UD9 continues to attract the curious.

“On Thursday, Friday and Saturday the line here is ridiculous,” said Anthony DeCristofaro, co-owner of both Alchemy and Lounge 215.

New Haven is the latest city to receive an oxygen bar. The trend began in Japan and made its first American appearance in cities with high air pollution, such as New York and Los Angeles.

“Basically, it’s very popular on the West coast, California, Las Vegas,” DeCristofaro said.

DeCristofano went on to say that he chose the oxygen bar to separate his clubs from other businesses in New Haven.

“We wanted to bring something new to Connecticut,” DeCristofaro said.

The flavors include popular favorites like Sex on the Beach, along with Chillin’, Eucalyptus, and Cloud Lime. The oxygen is delivered to patrons through nasal cannulas, two-pronged breathing tubes, which are discarded after each use.

After the session, which is capped at 20 minutes, comes a complimentary drink.

“For each session you buy you get a free acceleration shot. It will accelerate your oxygen experience,” said DeCristofaro, who added that the shots were all herbal.

Additionally, DeCristofaro attributed a wide range of health benefits to the oxygen sessions.

“It’ll cheer you up. Hangovers and headaches, it just kills them. It aids weight loss,” said DeCristofaro, adding that he believed the oxygen could increase alertness and stamina as well as clearing the lungs and liver.

Many doctors and scientists, however, are skeptical about the benefits of oxygen sessions. Since a healthy person’s blood is 99 percent saturated with oxygen when breathing normal air, many question what value additional oxygen could have.

According to the website of Medill School of Journalism at Northwestern University, there is no benefit to breathing supplemental oxygen. “You do need oxygen at the cellular level to maintain normal functioning of cells, but if you’re healthy, the level of oxygen you get from room air is enough,” said Dr. Manu Jain, assistant professor of medicine at Northwestern University Medical School’s division of pulmonary and critical care.

Perhaps after hours of being saturated with alcohol and cigarette smoke, Alchemy barflies want at least the illusion of a healthy activity. Offsetting the effects of alcohol was a common motivation for patrons trying the oxygen.

“I was drinking and it was really making me tired,” said Greg DeLuca, a frequent Alchemy visitor who had never tried an oxygen bar before. “I definitely feel different. I feel more aware, more alert, more energized.”

Several of the oxygen bar patrons were repeat customers. Jimmy O’Brien, who said he had an oxygen session at least once a week, described the effect the oxygen had on him.

“It kind of makes me feel clean and a little light-headed,” O’Brien said.