It looks set to shift up to 150,000 copies on the first day of its release on Monday, a store said. HMV said initial sales from the chain and other entertainment retailers suggested Boyle's debut album has been selling an amount that most major new albums would typically sell in a week.
The figure includes massive online pre-orders that have been placed by customers over the past few weeks.
HMV is revising its estimate for total weekly sales upwards, from the 300,000 that the retailer initially projected, to a figure closer to 400,000.
This would make the album the biggest and fastest-selling release of 2009. The sales would be comparable to those of Take That's The Circus in December last year, which sold 432,490 copies in its week of release.
The chain reported that sales are particularly huge in Scotland, where some customers are snapping up multiple copies.
HMV is now also predicting that the album will be the Christmas number one.
The store's Gennaro Castaldo said: ''The Susan Boyle story just keeps getting bigger and more fantastic.
''Our hmv.com online store had one of its largest-ever pre-orders for an album and now we're seeing a huge surge in demand in our stores, though especially in Susan's native Scotland.
''People of all ages seem to be buying it, and it's clearly going to be one of the must-have gift items this Christmas.
''Susan's accomplished performance on the X Factor has given the album a massive, timely boost, and it now has the momentum to challenge the likes of Leona, JLS and The Soldiers for the Christmas number one.''