A method for responding to order flow is disclosed. The method comprises establishing for a market maker a rule for automatically generating a contra order in response to an order. The rule comprises at least one condition comprising at least one characteristic describing the order. The at least one condition allowing matching based on a security in the order is in a security list specified by the market maker. The method further comprises receiving from a trader the order; matching on the computer the order to the at least one condition of the rule; automatically generating the contra order in response to the order, if the rule is satisfied; and providing the contra order for acceptance.