PayPal Inc. will launch Mobile Express Checkout, a version of its Express Checkout system already available to e-retailers, by the end of October. With it, consumers will be able to complete purchases on merchants’ mobile sites using their PayPal account.

PayPal representatives say the streamlined payment option will appeal to mobile shoppers because it limits the amount of data entry, such as credit card information and shipping details, consumers would have to enter on mobile devices, as these details are already stored with PayPal. When Mobile Express Checkout is an available payment option, the consumer will be able to click the PayPal button on the mobile site and will be taken to a PayPal site where she can log in, confirm her funding type and shipping information, and click to complete the transaction.

Mobile Express Checkout currently is being tested on the mobile commerce sites of Buy.com, Nike.com and FootLocker.com. The company says the mobile checkout system will be optimized for iPhone and Android versions 2.0 at launch, and will work on all mobile web devices by the first quarter of 2011.

The mobile version will only be available to e-retailers that use Express Checkout on their e-retail web sites, and e-retailers will pay the same fee—30 cents per transaction plus a fixed percentage of 2.2% to 2.9% of the sale value— to process Mobile Express Checkout payments as they do Express Checkout payments for conventional online transactions, says Stephen Strauss of PayPal. PayPal, which is owned by eBay Inc., expects to process more than $500 million in mobile payment volume this year.