Sotheby’s unveiled The Rare American Whiskey Selection 1976-1982, a unique set of five prototype bottles created in the mid-1990s.

These bottles were originally produced as the prototypes for the world’s first collectable ultra-premium U.S. whiskey series to exclusively feature closed distilleries in America. They will be auctioned April 14, and Sotheby’s calls the selection “the rarest American whiskey ever seen at auction.”

Here’s what is in the collection:

• Old Quaker Indiana Corn Whiskey 21-Year-Old Limited Edition Barrel Proof; 65% ABV (1976)
• Stitzel-Weller Kentucky Straight Bourbon Whiskey Limited Edition 17-Year-Old Barrel Proof; 53.5% ABV (1980)
• Taylor-Williams Kentucky Straight Bourbon Whiskey Limited Edition 17-Year-Old Barrel Proof; 56% ABV (1980)
• George T Stagg Kentucky Straight Rye Whiskey Limited Edition 16-Year-Old Barrel Proof; 57% ABV (1981)
• Buffalo Springs Kentucky Rye Mash Whiskey Limited Edition 15-Year-Old Barrel Proof; 62.5% ABV (1982)

The collection was the initiative of The Classic Kentucky Bourbon Company, a subsidiary of United Distillers, in 1997. United Distillery owned the Bernheim Distillery and Stitzel-Weller at that time, and once The Rare American Whiskey Selection project was approved for launch, it merged with another company, International Distillers & Vinters. The merger created United Distillers & Vintners, forming the spirits division of Diageo. At that point, the project was shelved, with no plans to revisit it.

The original premise of the Rare American Whiskey Selection was to create an annual release of five very different barrel-proof, high-age statement whiskies. The project got as far as bottling two examples of each of the selected whiskeys, with prototype labels, filled with the actual liquid to exhibit the finished product as it would be sold. The whiskeys were tasted not just within United Distillers when they were created, but also by respected industry critics at the time.

The two sets of whiskey were split up and, ironically, one set was sent to the Stitzel-Weller distillery for safekeeping, while the other set remained at the company headquarters in the U.K. for the European market. It is believed that the set at Stitzel-Weller was destroyed in the distillery fire, making the one set for auction the only one that still exists.

Initially scheduled to be offered in a limited run of 6,000 bottles per release, the set theoretically would have been a landmark in the history of premium American Whiskey. The project would have preceded the Buffalo Trance Antique Collection by a number of years and seen the footprint of U.S. Whiskeys in whiskey collector circles change dramatically.