Veteran rockers The Eagles have topped the US chart after a last-minute rule change by its compilers.
The band are known for hits such as Hotel California and Lyin' Eyes
Long Road Out of Eden was originally denied a place on the Billboard chart because it is sold exclusively in the US through retail chain Wal-Mart.
Previously, titles not on general sale in the US were not eligible to appear on the chart.
The 711,000 albums sold by The Eagles pushed Britney Spears's Blackout into second with 290,000 copies.
Spears would have been number one upon the release of final SoundScan figures on Wednesday morning.
However, Billboard said late on Tuesday that it had changed its rule and the Eagles album - the band's first studio work for 28 years - would be number one instead.
"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," said Geoff Mayfield, Billboard's director of charts.
A limited number of other artists may also enter the charts under the new system.
The rule to not allow exclusive releases to appear on the Billboard chart was imposed at the request of retailers and labels shortly after Billboard started using Nielsen SoundScan data in 1991.
In November 2005, Wal-Mart teamed up with country star Garth Brooks to sell an exclusive boxed set.
The retailer said at the time that Garth Brooks: The Limited Series sold more than 500,000 copies on its first day during the busy Thanksgiving holiday period, but the feat was not recognised by Billboard.