Revenue from mobile adult content is expected to reach $1 billion worldwide this year, driven by the increase in sophisticated services that deliver video clips and streaming video, in addition to text and images, a research firm said Friday.

The 50 percent increase in revenues predicted for this year over 2004 will mostly come from Europe and the Asia-Pacific regions, Juniper Research Ltd. said. But porn fans in North America, especially in the U.S., are expected to boost revenues past the $400 million mark by the end of the decade.

By 2009, the value of the global adult market in the mobile phone industry is expected to reach $2.1 billion, according to Juniper.

Currently, the size of the U.S. market is limited because wireless carriers are reluctant to offer adult content out of fear of a regulatory or consumer backlash, Juniper analyst Windsor Holden said. This holds back revenues because wireless subscribers are used to downloading content through their carriers' portal.

Until carriers offer adult services, however, people are expected to become adept at browsing wireless Internet sites operated by aggregators or other independent providers, increasing revenues significantly, Holden said.

Worldwide, small businesses are expected to dominate the market this year, but major adult publishers are encroaching on their market share, Juniper said. European customers are currently the biggest spenders on adult content, with an average annual revenue per user of more than $34.