Look out Las Vegas, here comes FarmVille. Silicon Valley is betting that online gambling is its next billion-dollar business, with developers across the industry turning casual games into occasions for adults to wager.

At the moment these games are aimed overseas, where attitudes toward gambling are more relaxed and online betting is generally legal, and extremely lucrative. But firms, from small teams to Facebook and Zynga, have their eye on the ultimate prize: The rich American market, where most types of real-money online wagers have been cleared by the Justice Department.

Two states, Nevada and Delaware, are already laying the groundwork for virtual gambling. Within months they will most likely be joined by New Jersey.

Bills have also been introduced in Mississippi, Iowa, California and other states, driven by the realisation that online gambling could bring in streams of tax revenue. In Iowa alone, online gambling proponents estimated that 150,000 residents were playing poker illegally.

Legislative progress, though, is slow. Opponents include an influential casino industry wary of competition and the traditional antigambling factions, who oppose it on moral grounds.

Silicon Valley is hardly discouraged. Companies here believe that online gambling will soon become as simple as buying an e-book or streaming a movie, and that the convenience of being able to bet from your couch, surrounded by virtual friends, will offset the lack of glittering ambience found in a real-world casino. Think you can get a field of corn in FarmVille, the popular Facebook game, to grow faster than your brother-in-law?s? Five bucks says you cannot.

?Gambling in the US is controlled by a few land-based casinos and some powerful Indian casinos,? said Chris Griffin, chief executive of Betable, a London gambling start-up that handles the gaming licenses and betting mechanics of the business for developers. ?What potentially becomes an interesting counterweight is all of a sudden thousands of developers in Silicon Valley making money overseas and wanting to turn their efforts inward and make money in the US?

Betable has set up shop in San Francisco, where 15 studios are now using its back-end platform. ?This is the next evolution in games, and kind of ground zero for the developer community,? Griffin said.

Overseas, online betting is generating an estimated $32 billion in annual revenue ? nearly the size of the US casino market. Juniper Research estimates that betting on mobile devices alone will be a $100 billion worldwide industry by 2017.

As companies eagerly wait for the US market to open up, they are introducing betting games in Britain, where Apple has tweaked the iPhone software to accommodate them. Facebook began allowing online gambling for British users last summer with Jackpotjoy, a bingo site; deals with other developers followed in December and this month.

Zynga, the firm that developed FarmVille, Mafia Wars, Words With Friends and many other popular casual games, is advertising the imminent release of its first betting games in Britain.