Yahoo Search Marketing and Virgin Group founder Richard Branson unveiled a contest for small-business owners on Thursday, offering 10 million free ad impressions on the Yahoo network to the winning entrepreneur who "thinks big," CNET reported. The Think Big contest will run April 28-May 20 and is open to U.S.-based entrepreneurs with fewer than 99 employees that operate a website. Those in the adult entertainment, gambling or travel-related businesses cannot take part. The pool of candidates will be narrowed to 100 semifinalists, then the top 5 among them. Branson will evaluate those and select the winner, which will receive 10 million ad impressions on Yahoo's network. Eight million of the ads will be on Yahoo sponsored search, and two million will be banner ads on the Yahoo network.