These futuristic concept cars from the 1950s are up for auction with a $20 million estimate

(CNN) A trio of rarely seen, futuristic concept cars from the 1950s are going up for auction at Sotheby's, with an estimated value of up to $20 million.

The Alfa Romeo B.A.T. Concept cars -- each with a distinctive sculptural shape that nods to fantasy and science fiction -- are described by the auction house as "amongst the most spectacular and memorable automotive designs ever produced."

The one-off cars, which were commissioned to showcase the radical design engineering and pioneering aerodynamics of the era, are being offered as a single lot for the first time, with an estimate of between $14 million and $20 million at the October 28 evening sale in New York.

Named B.A.T. 5, 7, and 9, the vehicles were created by Italian designer Franco Scaglione and manufacturer Carrozzeria Bertone before being unveiled to the public over three years at exhibitions in 1953, 1954 and 1955.

The cars were never shown together in the 1950s and were sold to separate collectors after being exhibited.

The trio were reunited briefly at the classic car show Pebble Beach Concours d'Elegance in 1989, after which they were bought by a single collector.

Even if the cars sell for the estimated $20 million, they won't be the most expensive to go on the block.

In 2018, a 1962 Ferrari 250 GTO sold for $48.4 million at RM Sotheby's annual Monterey collector car sale -- a world record for any car ever sold at auction.

The GTO had won the 1962 Italian GT championship, and notched up more than 15 race victories from 1962 to 1965.