Abstract: An auto substitution system and method are provided for facilitating fulfillment of intraday trading requirements by implementing collateral in encumbered shells of tri party repo agreements. The method is triggered upon notification of insufficient unencumbered collateral to satisfy delivery instructions for required collateral. The method includes receiving, at an auto substitution system, a request for the required collateral upon failure to locate unencumbered required collateral. The method further includes implementing computer processing components of the auto substitution system to search for the required collateral in the encumbered shells and upon finding the required collateral, searching for replacement collateral for the required collateral. The method further includes implementing the required collateral found in the encumbered shells to fulfill delivery instructions and substituting the replacement collateral for the required collateral found in the encumbered shells.