AALGAARD, Norway -- They compete to trick out the flashiest party buses, buy enough beer to level a biker club, and commission crude songs to soundtrack their graduation blowouts. And that's before they even take their exams.

They are "the russ," teenagers on the verge of graduating from Norway's high schools, and they have a tradition of rocking the rite of passage in their otherwise temperate country with a level of drunken revelry that tips the international scale.

Dressed in red and blue overalls adorned with the Norwegian flag and matching emblems of school spirit, russ -- short for the decadent senior celebrations called "russefeiring" -- fill town streets by day and party at night for a month each year leading up to Constitution Day on May 17.

"In the American movies, we get the impression that they are so crazy. But we have the craziest celebrations here in Norway," Fredrik Helgesen, a student leader of the russ committee at a school west of Oslo, said. "I don't think anything in the world is like this."

The biggest bash happens each year at Kongeparken, a theme park on the outskirts of oil-rich Stavanger. During a three-day festival -- think California's famed Coachella transported from the desert to the snaking fjords by the icy North Sea, Norway's biggest music acts perform for 13,500 teens ready to rave at all costs.

Here, professionally painted coaches and double-decker buses line up, blasting specially commissioned music tracks from six-foot speakers or park in rings rigged with shared lighting, sound systems and DJs to create mini outdoor dance stages.

Driven around the country by professional drivers who can double their earnings taking a month-long sabbatical from their day jobs, the buses are less a method of transportation than discos on wheels. They often are kitted out with newly upholstered sleeping space for 20, laser lighting systems and speakers blasting bass so loud it makes your beer jump out of its glass.

Each bus has its own rap and techno tracks, sometimes as many as five, that cost up to 100,000 NOK ($12,000) each. With the cost shared between 15 and 25 students, the most expensive buses can run up to 3 million NOK ($350,000). The standard budget is just north of 1 million NOK ($116,000).

In the spirit of competition, the price tag for all the partying has spiraled up in recent years. Eirik Langoey, of Bergen, says his group's Russbuss Ghost Town is the best in the park. Like most of the graduates who have splashed out, he says the group worked and saved hard to afford it.

Others, like Erland Nesse from nearby Sandnes, whose group Pattaya spent some 2 million NOK on their Russbuss, admit that wealthy parents were instrumental in making it happen.

The "russefeiring" tradition dates back to 1905, when Norway gained its independence from Sweden. But the revelry among the russ has ratcheted up in recent years.

The craze for blingy buses began in the wealthiest parts of western Oslo around ten years ago, where the competition between schools and classmates is highest. But the fashion has begun to catch on in other parts of the country too.

The partying starts when classes end in the middle of April and lasts until Norwegian National Day on May 17. Exams begin shortly afterward.

Painful injuries can be common. Wearing a heavy arm splint as he sits on the grass beside friends waiting for an afternoon concert to start, Jon Slettan tells how he drunkenly broke his collarbone a day earlier and is keeping himself medicated now with both beer and painkillers, a potentially dangerous combination.

But serious injuries are mercifully rare. Aasmund Lund, one of the Kongeparken festival organizers, said he would rather be responsible for 13,500 18 and 19 year olds than 100 40 year olds.

While older generations mostly tolerate the russ, the month-long tradition and its expense can cause tongues to cluck in unflashy, egalitarian Norway. The boastful and sometimes misogynistic lyrics in the music also have drawn some negative headlines.

Most of the teens understand the concerns, but ask for understanding.

On a chair beside his bus, surrounded by cheering friends who grew up together and "sacrificed a lot to make it happen," Eyoub Yemane from Stavanger says the dying embers of youth deserve to be fanned hard.

"I would say you only do this one time. You are only allowed one time, so do it right when you graduate because you never go back here. Never," Yemane said.