The new Eminem album is set to be the UK's fastest selling CD of the year so far, according to early indications from record shops.
Eminem's record label said the album was selling "incredibly well"
The release of Encore was brought forward by three days to Friday after it appeared on the internet.
It is on course to sell more than 300,000 in two days and be number one in Sunday's chart, according to HMV.
That would put it ahead of new releases by Britney Spears and Westlife, which have both been on sale since Monday.
Eminem's first single from the album, Just Lose It, is currently number one in the UK singles chart.
A spokesperson for the rapper's record label Interscope said Eminem's fourth album was selling "incredibly well" but could not give figures.
An HMV spokesman said in just two days, Encore could challenge the 320,000 sales Robbie Williams' Greatest Hits achieved in its first week in October.
HMV head of music Mark Noonan said: "To grab the number one spot with just two days of sales, especially ahead of such a strong release as Britney's Greatest Hits, would be pretty unprecedented.
"But to outsell someone like Robbie in less than half the time would be just phenomenal, if it happened."
A spokesperson for Virgin Megastores said it was selling "phenomenally well" and they thought it would be number one on Sunday.
But internet shoppers were not so enthusiastic - on Friday, Encore was at number eight in online retailer Amazon's UK album chart, behind Pop Party 2 and The Scissor Sisters.