Google will launch a far-reaching online payments system today, after more than a year of speculation.

The system will be called Google Checkout, not Gbuy as rumour had it, and will be launched as a completed version, rather than a typical Google 'beta' offering. It will not be limited to Google advertisers, although participants in Google's AdWords program will have some advantages.

"This is a very big deal. This is an entire transaction ecosystem," said Gartner analyst Allen Weiner. "This is one of Google's most important deals in a long time."

In a nutshell, Google Checkout has been designed to simplify and streamline business-to-consumer e-commerce transactions by letting buyers store their purchasing information with Google. That way, users can store contact details, payment preferences and shipping information once, instead of having to enter that information separately with multiple merchants.

Google Checkout supports a variety of payment methods, including credit cards from Visa, MasterCard and American Express.

Meanwhile, Citibank cardholders who enroll in Google Checkout and make at least one purchase before 15 September will receive either a credit on their statement, cash back or reward-program points.

Google Checkout provides shoppers with a purchasing history and reimburses them for unauthorised purchases, said Google. Beyond the convenience for shoppers, Google Checkout will take advantage of, and potentially boost, Google's search and advertising services.

Merchants who participate in the program and also advertise on AdWords will have their ads run with a Google Checkout icon.

These merchants will be able to process for free a sales amount equal to 10 times the amount they spend on AdWords advertising. Thus, Google Checkout can potentially help Google grow its advertiser base. It also enhances the search services by adding a transaction-processing feature to searches centered on product purchases.

The program will not be limited to AdWords advertisers. Those non-AdWords merchants will be charged a flat fee for all transactions.

Google will offer several ways for merchants to integrate their websites with Google Checkout. At the simplest level, a company can include Checkout 'buy' buttons by pasting HTML code into their web pages. For more sophisticated integrations, Google will offer a Google Checkout API (application programming interface).