The album features 13 tracks by the pop star, including the now familiar "Womanizer," which was previously released, as well as other songs such as "My Baby," "Unusual You" and "Kill the Lights."

Releasing songs on the Web increasingly is being used to promote musicians and their work ahead of an album release, and Spears' "Circus" is among the most anticipated CDs of this year as she rebounds from a tumultuous 2007 and early 2008.

Spears, 26, went through a bitter custody battle over her two sons last year, exhibited strange behavior in public and by early 2008 was hospitalized twice for psychiatric evaluation.But in recent months her father, Jamie Spears, has assumed control of her business and personal affairs, and Spears seems to have turned her life around. The ability to complete and promote "Circus" is an indicator of her apparent health.

The full album will be released in stores on December 2, Spears' 27th Birthday.

Imeem has previously released music from recording artists including Fall Out Boy, U2, Lil Wayne and The Rolling Stones.