Some bared flesh and threw beads on Bourbon Street in the French Quarter, while others wore costumes lampooning the BP oil spill or other headline-grabbing events. Overall, this year's Carnival season has been among the most raucous since Hurricane Katrina, partly because it overlaps with many colleges' spring breaks.
Clarinetist Pete Fountain kicked off street parading shortly after dawn with his marching group. The traditionally African-American Krewe of Zulu and the parade of Rex, King of Carnival, followed. Mayor Mitch Landrieu led Zulu on horseback before dismounting at the antebellum-columned Gallier Hall for champagne toasts with Mardi Gras royalty.
The party would go on until midnight, when Carnival is replaced by the Christian season of Lent.
For many, the fun came in watching costumed partiers - and their themes.
A troupe of black-clad skeletons known as a Bone Gang paraded through the streets in a tradition dating from the 1800s that has voodoo overtones.
"The idea is it's kind of a warning for people in the neighborhoods, for the children in particular, to live right because we're all going to die," said Michael Crutcher, a Bone Gang member and college instructor.
In the Treme neighborhood, Ashley Scharfenstein, 24, dressed as a peacock with a black corset. She was jiving to the music at the street party, then strolled off to the French Quarter.
"Wherever the music takes us, we're going," she said.
Other costumed groups added political barbs to their revelry. In Bywater, walking clubs gathered for the annual saunter to the Quarter known as the St. Anne's parade.
"This is what Mardi Gras is all about, lampooning," said Pat Kent, a retired hospital executive clad as a gun-toting priest. He and a friend were going as the "krewe of guns in church."
"Today I'm packing for Jesus," he said. Kent said his costume was in protest of a new Louisiana law allowing people to carry weapons in church.
Nearby, the occasional clown, a Moammar Ghadafi lookalike, women in flowing dresses and a Roman soldier gathered.
In the French Quarter, satire was in bloom as maskers took aim at last year's BP oil spill in the Gulf of Mexico.
Allen Logue, 58, was clad as a one-man oil spill clean-up crew. The oil field consultant from Barataria, La., didn't have to do much shopping to build his costume. He already had a hard-hat helmet and BP-branded sweat shirt from work he did for the company in Alaska.
"The only thing I had to shop for was the Jim Beam and that was to ease the pain of the oil spill," Logue said.
Logue also carried super-absorbent kitchen napkins to clean any mess he might encounter, though the most likely spill on Bourbon Street would be beer and not crude oil.
For Paul and Amy Maudive of Long Beach, Calif., coming to Mardi Gras has been a tradition since 1976. Each year they dress in an Elvis-themed costume. After Hurricane Katrina they wrapped themselves in the blue tarps that covered so many blown-away rooftops, and last year they billed themselves as Elvitar, in tribute to the movie "Avatar."
This year, they were all oil spill.
Dressed in oil-stained jumpsuits with Elvis-style capes, they'd glued plastic birds and crabs to their costumes.
Sylvia Beyer, 57, of New Orleans led a group of 5 women in grass skirts and hats with the BP logo. On the back of their shirts were slogans, such as Broken Promises, Brazen Polluters and Bloody Pathetic. As they walked along, they passed out makeshift voodoo dolls with a photo of former BP CEO Tony Hayward pasted to each.
"We just wanted to stick it to BP. We put more time into these costumes than BP did in their disaster plan," Beyer said.
Hal and Sharon Moser of New Orleans mocked the new national healthcare program with their outfits. Hal Moser strolled along Bourbon Street dressed in a hospital gown with bloody bandages and a fake ax pasted to his head. "I've got a split-open headache from it," Moser said. His wife dressed as a nurse.
The Transportation Security Administration also took hits. One group outfitted as TSA inspectors carried signs referring to body cavity searches.
John Chapman of Mandeville, La., tried a different approach. He dressed as a Chilean miner, complete with an escape pod attached to his back.
Locals were in a triumphant mood, and not without reason.
New Orleans - America's poster child of disaster - has come a long way since Hurricane Katrina. Its beloved New Orleans Saints won the Super Bowl last year and it has largely overcome the disaster of the BP oil spill.
This year, the timing of Mardi Gras helped. It fell later than usual and coincides with spring break for college students. Students have been out in force - giving more punch to the annual pre-Lenten celebration.
Two friends on spring break from Wilmington College made a 12-hour drive from Ohio.
Garret Lingoe, 21, a junior, clutched a beer at midmorning Tuesday as he talked in awe of Mardi Gras. "I didn't know I was coming here until about 5 days ago and I'm sure happy I did."
Seth Howard, a 23-year-old senior, echoed his sentiments. "Everybody down here is just so nice and laid back."
Ali Miller, 23, an early childhood education major at Southeastern Louisiana University, was jubilant as she walked Tuesday morning after a long night of drinking in the French Quarter.
"There is nothing like New Orleans," she said. "I would never ever want to grow up anywhere but here! And Mardi Gras is the craziest time you could ever have in life - I don't know what else to say."
Mardi Gras was being celebrated across the Gulf Coast, in cities including Mobile, Ala., and Biloxi, Miss. In the Cajun country of southwest Louisiana, masked riders on horseback continued the tradition of riding from town to town making merry along the way.