A revision of Billboard’s chart policy has landed the Eagles’ first album in 28 years at No. 1, displacing Britney Spears’ own comeback effort to No. 2.

“Long Road Out of Eden,” the Eagles’ first studio album in nearly three decades, debuted at the very top of the Billboard 200, following the implementation of a chart policy change.

Billboard announces on its website that it will now allow exclusive album titles that are only available through one retailer to appear on The Billboard 200 and other charts. The change, effective with this week’s charts, was made “in consultation” with Nielsen SoundScan.

Preliminary figures show that “Eden,” which is currently available in Wal-Mart and Sam's Club stores, as well as at walmart.com and on the Eagles' own website, sold 711,000 units.

Pop princess Britney Spears’ own album, titled “Blackout” and released via Jive Records, would have debuted at No. 1, with first-week sales of 290,000 copies, nearly a third of the copies “Eden” sold.

Nielsen SoundScan data are to be issued on Wednesday and Jive’s initial estimation of sales between 330,000 and 350,000 copies during its first six days could still be confirmed.

Despite abundant and confusing media reports about her chaotic personal life that have been following Spears around over the past year, her fans have proved themselves loyal to the pop princess, helping “Gimme More,” her first and for the moment only single from the new album peak at No. 3 on Billboard's Hot 100 singles chart.

Her previous release, “In the Zone,” debuted at No. 1 in November 2003 with 609,000 copies.

The Eagles’ double album marks the second biggest opening sales week of the year, behind Kanye West's “Graduation,” which moved 957,000 copies in September.

“We know that some retailers will be uncomfortable with this policy, but it was inevitable that Billboard's charts would ultimately widen the parameters to reflect changes that are unfolding in music distribution,” Geoff Mayfield, Billboard's director of charts, said.

“We would have preferred to make this decision earlier, but only became aware within the last 24 hours that Wal-Mart would be willing to share the data for this title with Nielsen SoundScan.”

Among the changes that Billboard's director of charts refers to are Radiohead’s surprise release of their new album “In Rainbows,” as a download from its website for a price the fan can decide on freely – even nothing. There is also Madonna’s recent partnership with Live Nation, the world's largest concert promoter, that includes future albums.

The Eagles’ own “Eden” is a change from tradition, as it will be available exclusively through Wal-Mart and Sam’s Club store during its first year of release and on the band's website.

Things are a-changing.