Online gambling revenues reached 10.9 billion dollars world-wide last year even though betting is illegal in many countries including the United States, a survey showed.
The research firm eMarketer said global Internet gambling revenues - minus the amounts paid to winnners - grew 28 percent last year.
The strong growth comes even though many players keep their cards close to the vest, eMarketer said in a report.
In the US, eMarketer said surveys show divergent results on who gambles online.
One report indicated as many as 15 percent of all US Internet users visited gambling or sweepstakes sites at least once a month. But a Harris Interactive survey suggested some 95 percent of US residents never spent money at online casinos or other betting sites.
"One suspects that if online gambling were legal in the US, online users would have been less hesitant to admit to gambling online, and the poll numbers would be considerably higher," the eMarketer report said.
Asked if online gambling should remain illegal in the US, users were roughly divided, with 53 percent saying it should remain banned and 47 percent favouring legalisation.