Digital marketing agency AKQA has started quietly courting potential buyers and could be sold to one of the biggest Madison Avenue firms for as much as $150 million.

The company's majority owner, Francisco Partners, a $3 billion private equity firm, has been shopping AKQA and could eventually decide to engage an investment bank to officially shop the company, according to the New York Post (via MediaPost).

Sources familiar with AKQA put its revenue at $75-$100 million, saying its VC backers want to set the price at 1.5 times that. Those potentially interested reportedly include WPP, Publicis and Omnicom, along with interactive shops aQuantive and Digitas.

The San Francisco-based company, which designed the interface of Microsoft's Xbox gaming console, has 475 employees worldwide and clients such as Nike, Visa, Microsoft, McDonald's and Unilever. AKQA was named "Interactive Agency of the Year" in the U.S. by Creativity Magazine and the Revolution Awards in the U.K.