The singer's sixth studio album, released on her 27th birthday Dec. 2, sold 505,000 copies and is her fifth No. 1 debut on the Billboard 200 chart. Circus' totals, the seventh-highest of 2008, dwarf sales of Spears' 2007 Blackout, which moved 289,000 copies in its first week and has sold only 926,000.

Two top 10 pop singles —Womanizer and Circus— and a spate of positive news have helped fuel the turnaround.

"People are just loving how she is doing right now," says Barry Weiss, chairman and CEO of the BMG Label Group.

Spears began the year being hospitalized for psychiatric evaluation after refusing to relinquish custody of her two sons to ex-husband Kevin Federline.

Soon after, a judge placed her affairs under the co-conservatorship of her father, Jamie Spears, and she reunited with former manager Larry Rudolph. She also reached a custody settlement in July. Weiss credits her father and Rudolph for getting her back on track.

She made two appearances on TV's How I Met Your Mother and triumphed at MTV's Video Music Awards (2007's appearance was a disaster), winning three trophies. More recently, she performed Circus on Good Morning America and was seen on the MTV documentary Britney: For the Record.

Sean Ross, Edison Media Research vice president of music and programming, says Circus has benefited by more positive circumstances.

"By the time Blackout came out, (hit single) Gimme More was grinding to a stop at radio," he says. "The publicity around her was relentlessly negative. By comparison, we've had six months of 'Britney is back' publicity."

Kim Davis, programming manager for AOL Music, says Spears has been bolstered by an aggressive online campaign that has lured younger fans.

"And she's like old Britney with the long blond hair, toned-up body and making sexy videos, and that's resonating with her old fans," Davis says.

Weiss says the star deserves credit for knowing her audience well and changing with the times:

"Despite all the craziness and paparazzi and people chasing her around, she's not that dissimilar to a lot of the girls buying her records."