Keen to market its latest gas-guzzler by the trick of online viral marketing, American car company Chevrolet introduced a Web site allowing visitors to take existing video clips and music, and then insert their own words to create a customised 30-second commercial for its 2007 Chevrolet Tahoe model.

But what happened next is hilarious and not what Chevrolet had in mind. One ad reads. ”Our planet’s oil is almost gone, you don’t need G.P.S. to see where this road leads.’’ Another: ”Like this snowy wilderness? Better get your fill of it now. Then say hello to global warming.”

A spokeswoman for Chevrolet, Melisa Tezanos, told the New York Times. “We anticipated that there would be critical submissions. You do turn over your brand to the public, and we knew that we were going to get some bad with the good. But it’s part of playing in this space.”

Go on have fun and make your own ad: