New open-top Bentley Mulsanne previewed.

The Bentley Mulsanne range will grow to include a convertible model if potential customers give the seal of approval to a dramatic concept version. The Mulsanne Convertible Concept, depicted here in these official sketches, was shown behind closed doors to existing and potential Bentley customers at the Pebble Beach Concours d’Elegance in California last weekend.

An insider described the open-top Mulsanne as “a logical expansion” of the Mulsanne range given Bentley’s rich history of creating luxurious four-seat convertibles. There has been no such car in Bentley’s line-up since the Azure went out of production in 2010. The concept is described as “not just whim and fancy” by our insider, and is “quite a long way towards being production viable” despite its conceptual appearance in these sketches.

The Pebble Beach reveal is significant, as North America — and even more specifically California — has traditionally been the key world market for cars in the luxury four-seat convertible segment.

Sales of the two most recent big Bentley convertibles — the Mk1 Azure produced between 1995 and 2002, and the Mk2 made between 2006 and 2010 — have mostly come from North America. Of the 1300 Mk1 and 800 Mk2 Azures sold worldwide, 700 of the former and 800 of the latter went to North American customers.

Should the latest open-top Bentley find favour among those invited guests at Pebble Beach, it’s conceivable that it could go into production fairly quickly — possibly within the next two years — given how eagerly its production readiness has been talked up.

The growing importance of China to Bentley should also be part of the calculation on whether or not to put the concept into production. In the first half of 2012, Bentley sales in China were up 55 percent to 1059 units, putting it a close second to North America in the Crewe firm’s global sales tally.

No technical details of the concept are known, but the sketches do reveal key highlights. For example, the convertible is likely to share its basic front-end look with the four-door saloon on which it is based. But it will feature more muscular rear haunches, long doors, a sleeker profile and a rakish rear end to distinguish it as a very different type of Mulsanne.

The dimensions of the concept are also unknown, but the most recent Azure shared its wheelbase with the Arnage on which it was based, and this policy is likely to continue with the Mulsanne. The result will be a convertible with formidable road presence that’s likely to be around five and a half metres long and two metres wide, similar dimensions to the Rolls-Royce Phantom Drophead Coupé’s.

The sketches also reveal that Bentley will stick with the soft-top roof that’s been a hallmark of convertible Bentleys over the years, rather than switch to a costlier and heavier retractable hard-top. Under the bonnet is expected to be the mighty 6.75-litre twin-turbocharged V8, delivering 505bhp, taken from the Mulsanne saloon.

Bentley’s soon-to-depart chairman and chief executive, Wolfgang Dürheimer, describes the Mulsanne saloon as “the perfect foundation on which to create the world’s most elegant convertible”.

“The Convertible Concept will extend the appeal of the Mulsanne family, while enhancing the profile of the Bentley brand, particularly in new and emerging markets,” he added.

Insiders are talking down the prospect of a Mulsanne coupé at this stage, but it’s another likely addition to the line-up as Bentley seeks to extend the Mulsanne range.