Google has opened up its Gmail Web mail service to more users by randomly offering accounts to some visitors to

Until Monday, to get a Gmail account, a user had to be invited to the service by either Google or an existing Gmail user.

"We just started (on Monday) offering Gmail accounts to a randomly selected sample on Google," said Marissa Mayer, Google's director of consumer Web products. "It's a natural step to leverage the wider user base of to grow Gmail."

About one in 20 visitors are getting the Gmail account offer, Mayer said. "Based on the success of this one-in-20 scope, we'll be ramping it up over the next couple of weeks," she said.

Gmail, a free service, is still in a beta, or test, phase, but there has been much speculation about when it will be launched officially and opened up to Web users in general.

Gmail rocked the Web mail market when it was announced in April 2004 due to its then unprecedented 1GB inbox storage. Since then, webmail providers large and small, including big players Microsoft and Yahoo, have reacted to Gmail by increasing their inbox storage capacity.

Gmail also brought Google a good amount of controversy due to its inclusion of contextual text ads in the messages based on their content, which prompted privacy advocates to criticize the practice. Google defended itself by saying that the ads are generated automatically with text-scanning technology and without human intervention.