The Hong Kong Transport Department began auctioning vanity car plates in 2006. Since then, the car owners in the buzzing, wealthy financial and trading city have spent many millions of dollars at the auctions, held about once a month.

Some of the highest prices ever fetched at auction anywhere in the world have been achieved in Hong Kong, according to Regtransfers.co.uk, a company that deals in car registrations in Britain, one of only a handful of countries where new license plates are auctioned by the authorities.

Those interested in a personalized registration plate file a request for their dream combination with the Hong Kong Transport Department. The combinations are then auctioned. If no rivals emerge, the plate goes to whomever put forward the request, for the minimum price of 5,000 dollars. Some combinations, however, set off bidding wars, occasionally pushing prices to stratospheric levels.

The record for Hong Kong was the plain number “18,” which fetched 16.5 million dollars in 2008. At the more modest end of the scale, “TAX1,” which sold for 75,000 dollars in July 2008, can be spotted in Hong Kong’s crowded streets on, yes, a humble taxi.

Numbers deemed lucky — eight is especially auspicious — as well as two- and three-letter initials are also very popular, and can command tens, if not hundreds, of thousands of dollars.

Few of these simple and desirable combinations now remain for the Transport Department to auction off, however. The last sale was dominated by more awkward combinations, such as “1 HAU 1,” “J21L” or “CHY 21,” which all went for the minimum price of 5,000 dollars.

“Car plates that go up for auction now are highly personalized, so many of them only go for 5,000 dollars,” said Mr. Chu, the license plate trader. The lower auction totals, he added, are “not really related to how the economy has been doing.”