A message prioritization process includes an interface process for receiving a primary attributable security interest message and one or more secondary attributable security interest messages placed by the market participant on a securities trading system. The primary attributable security interest message relates to a defined quantity of an individual security traded on the securities trading system. Each secondary attributable security interest message increments the defined quantity of the primary attributable security interest message by an incremental quantity. A code assignment process assigns a superior prioritization code to the primary attributable security interest message and an inferior prioritization code to each secondary attributable security interest message. These prioritization codes control the order in which the attributable security interest messages are processed by a matching process, and the inferior prioritization code is subordinate to the superior prioritization code.