A half-graphical user interface (Half-GUI) order processing (HGOP) system with single sign on and its method of use is described. A set of web services may be utilized for order processing in an electronic commerce system which allows a merchant to host a product catalog and shopping cart, but post the transaction to an e-commerce system in one simple transaction. In response to a shopping cart request and utilizing single sign on technology, the HGOP system exposes a single checkout form, prepopulated with customer account information to a merchant web site. If no edits are required, the transaction posts and an order confirmation/thank you page is displayed. If edits are required or a new customer account is required, the customer's account is updated or created.