Auctioneer Bonhams & Butterfields is giving natural history buffs the chance to own "Samson", a fossilised female Tyrannosaurus Rex.
Samson's 170 bones were discovered 17 years ago in South Dakota, US, and make-up more than half the skeleton of the 40-feet-long, 7.5 ton dinosaur.
Bids are hoped to top $6m when it is sold at the Venetian hotel-casino in Las Vegas, on October 3.
The sale will also include hundreds of bone fragments in plastic bags - these separate bones could be added to Samson if experts are willing to invest the necessary thousands of hours.
The T. Rex is being sold among 41 other lots of museum-ready pieces, including a 28-foot duck-billed dinosaur skeleton and a seven-feet fossil shark.
The collection will be on public preview for two weeks before the auction.
A similar T. Rex fossil - named "Sue" - sold in 1997, for $8.3m. It can now be found at the Field Museum in Chicago. Sue is 42 feet long with more than 200 fossilised bones.
Samson is the third most complete T. Rex skeleton ever discovered, according to Tom Lindgren, a natural history expert for Bonhams & Butterfields.
The dinosaur is also one of only 42 specimens discovered in the last 100 years with more than 10% of its bones.
Most major museums in the world only have casts of T. Rexs, rather than the real thing.
Samson's bones have been stored in a warehouse and have never been exhibited privately or publicly, said Mr Lundgren.
The bones were excavated in 1992, after the son of a rancher found the female T. Rex's lower jaw in 1987. The bones have previously been sold twice to private buyers and currently has an anonymous American owner.
The owner apparently paid more than the $6-8m the bones are expected to sell for this time around - the conservative estimate is due to the skeleton being mounted on a frame designed specifically for scientific study.
"Sue" was sold unmounted in 1997.
It is hoped that the skeleton will end up in a museum of scientific institution for further study and display - although private buyers are also welcome to bid.