At almost 300 years old, somewhat moldy from the remnants of Hurricane Katrina and surrounded by muddy water and swamps, this city is not exactly known for being lemony fresh.

The signature scent around Bourbon Street, after all, is the smell of spilled liquor.

But from the French Quarter to New Orleans East, people here have been complaining about a tinge to the air that is unsettling even by local standards.

Many suspect that it has something to do with the oil disaster in the Gulf of Mexico, which has already leaked millions of gallons of crude about 50 miles off the Louisiana coast. The authorities involved in the cleanup of the fallen Deepwater Horizon oil rig have been burning oil on the surface of the gulf and using chemical dispersants around the leak.

Could New Orleans possibly be smelling that, from more than 100 miles away? Many say yes. But the mystery odor, which is stronger on some days and in some areas than others, is hard for residents to describe.

"It's chemical, and I'm trying not to think about it," said Raymond Dillon, a karate teacher.

Diana Mecera, a restaurant worker who lives in the French Quarter, said, "It's a kind of a sewage smell."

Her co-worker, Lauren Graham, a waitress, put it this way: "It's more like being at a gas station."

Steven Payne, who owns a men's store and lives in the Marigny area, said: "It is very distinctly oil. When I smelled it for the first time, I was walking my dog along the Mississippi River levee."

Some people who do not notice anything in particular about the scent of the city these days have suggested that their fellow New Orleanians are perhaps a bit overly sensitive.

"It's paranoia," said Lee Washington of New Orleans East. "I sit outside every day, and if I smelled oil, I'd say so."

And that is part of the problem: it is too subjective, said Jeff J. Dauzat, a scientist with the Louisiana Department of Environmental Quality. "You try to tell someone you don't smell it," he said, "and they say, 'You're crazy!' But the only thing that can overcome emotion is fact."

And the facts say the air is safe. More than 800 air samples are being tested every day by the state's scientists, the federal Environmental Protection Agency and private contractors hired by BP, Mr. Dauzat said, from the shoreline to the population centers farther inland.

Air safety, however, has little to do with its smell, which Mr. Dauzat acknowledges could drift in more than 100 miles from the gulf under certain wind conditions.

He cautioned that this was an area with a lot of refineries, chemical plants and cargo shipping, which could all contribute to the smell of the air.

"We can't say the complaints of the odors are not valid," Mr. Dauzat said. "But just because you're smelling it doesn't mean it's at a harmful level."

He added: "It may be unpleasant to hang out outside, but will it kill you? No."

Larue Hatten, a resident of the French Quarter, said he had not noticed anything unusual lately.

"Frankly, I'm more concerned about what the oil is doing to the gulf sea life and shoreline than the smell, personally," Mr. Hatten said. "And here in the Quarter there are so many smells. It's hard to know what's what anyway."