A method of operating a computer system includes storing attributes of a buying organization, vendors, invoices and/or line-item details from invoices in one or more databases. Rules are established for selecting settlement options for the invoices. The rules are applied such that the computer system selects a first one of the settlement options to settle a first one of the invoices rendered by one of the vendors, and the computer system selects a second one of the settlement options to settle a second one of the invoices rendered by that vendor.