American tourists have long been fans of London's roomy black taxicabs and their colorful drivers' gift of gab. But these days, tourists can expect more than a memorable journey and forceful opinions.

They can expect a sales pitch.

Drivers of black cabs are being recruited as the latest weapons of businesses seeking to use word-of-mouth advertising to entice passengers to buy their products or services.

"Drivers spend an average of 16 minutes with a passenger and that's a lot of time for someone to have with a captive audience," said Asher Moses, managing director of Taxi Promotions UK, the agency that facilitates the ad campaigns.

Already about a dozen drivers have been recruited to promote an online gambling business, while another five have been called upon by the Tourism Authority of Thailand to talk about the benefits of traveling to that country.

By the end of the year Moses expects to have as many as 300 cab drivers involved in marketing schemes across Britain.

"Obviously you can't bombard passengers with a bunch of brand awareness messages," Moses said. "But a driver can tell if a passenger will be receptive to having a conversation."

For example, in the promotion orchestrated by Thai tourism authorities, drivers might comment on London's dreadful weather.

The passenger's response will enable drivers to get a sense of that passenger's receptiveness to hearing a sales pitch.

"Drivers can go on to talk about holiday destinations that are nice and sunny and then go on to say something about Thailand," Moses said. "Drivers can tell if a passenger is willing to talk or if they just want to sit and read a newspaper or stare out the window."