Moses Oakland stood under the spotlight at Famous Dave's BBQ & Blues in Uptown's Calhoun Square on a recent Sunday evening. Electric guitar slung over his shoulder, the veteran blues player scanned a sheet of paper with a list of names scrawled on it.

"Brian the guitar player, you out there?" Oakland said into the microphone. "Brian the guitar player, come on up."

Brian Martin, 20, popped up from his seat . His friends cheered as he fished a Fender Stratocaster from somewhere under the table. He joined Oakland and the rest of the house band onstage, plugging in his guitar and tuning up.

A few moments later, Oakland kicked into the first bars of "Hoochie Coochie Man." Martin, a 20-year-old Marine home in Minneapolis on leave , was instantly jamming along, helping the band stomp its way through the classic blues number.

The scene at Famous Dave's has become a familiar one. Almost every night of the week, an open blues jam is going on at some Twin Cities area bar or restaurant.

"Blues jams seem to be riding a popularity high," said Oakland, 52, who began hosting them at the now-defunct Blues Saloon in St. Paul in the late '80s. When he first moved to the Twin Cities from California in 1987, there were maybe two or three blues jams a week, but that number skyrocketed in the early '90s.

"The blues in general was having a renaissance then," Oakland said. "More and more venues were calling themselves blues clubs or booking blues acts."

While the growth of new blues jams has leveled off, the demand has stayed steady. Some clubs require performers to be 21 or older, but not all. And typically, there's no cover charge for a jam.

"One thing blues jams do is let clubs know there is an interest in blues out there," says Pete Takash, an interim board member of the newly formed Minnesota Blues Association. "They're also great for fans because it gives them a real sense of what's going on."

The jams started in bigger cities like Chicago and New York in the mid-1990s as a way to fill clubs on Monday nights, which traditionally were dark. "The musicians who had nothing else to do on Monday night would gather at one of the clubs and have an impromptu jam," Oakland said. "This became known as the Blue Monday jam. It evolved from there."

Blues jams now offer anyone with enough courage the chance to step onstage and demonstrate their talents to a live audience. Oakland's jam at Famous Dave's can feature anywhere from 10 to 30 musicians a night as people sign up stating what instrument they'd like to play or what song they'd like to sing.

A house band usually will host the jam and call up each participant for a song or two. Regulars — or those who instantly click with the house musicians — will often get asked to sit in for an entire set. As with any open-mic night, some musicians are instantly in over their heads. Other times, a stranger will walk into the bar, plug in a guitar and completely blow Oakland away. The best part of doing it, he says, is that even he doesn't know what will happen on any given night.

"We once had a whole gospel choir come down to Famous Dave's," he said. "There were 40 members. They had been out performing and had come here to rib up afterward. They heard us playing and said, 'Can we sit in?' We brought them up onstage, and they tore the joint up."

While he was only one man with a guitar on Sunday night, Martin still gave the audience plenty to cheer about, bouncing around the stage and working through leads.

As he packed up his guitar and prepared to watch the rest of the evening from his seat halfway back from the stage, he still had a smile on his face.

"I just love feeling the music," he said, "being up there jamming."

John Nemo, a free-lance writer from Woodbury, can be reached at johnnemo@attbi.com .