The second DVD version of The Lord of the Rings: The Two Towers is thought to have sold at least 750,000 copies in the US on its first day in the shops.
The final Lord of the Rings film is released in cinemas next month
The Hollywood Reporter industry paper quoted video industry sources as saying it sold between 750,000 and 1m copies.
The four-disc set includes an extra 43 minutes of footage as well as other features.
A spokesman for UK retail chain HMV said the DVD set was number one in its sales charts "by a mile".
Genarro Castaldo told BBC News Online: "It's flying off the shelves.
"It's got real cult appeal, and it's building up nicely for the theatrical release of the next Lord of the Rings film next month, mirroring what happened this time last year."
The final film in the Rings trilogy, The Return of The King, is released in the US and UK on 17 December.
Back in the US, Arnold Schwarzenegger's Terminator 3 DVD and video topped the sales charts, its release coming the day after the actor's inauguration as governor of California.