An automated system for matching orders to buy and sell securities at the midpoint of a best bid and offer (“BBO”), wherein the automated system is adapted to (i) operate on a fully-anonymous and continuous basis, (ii) process multiple, computer-generated orders, of any size, transmitted by algorithmic, program, and other automated trading systems, (iii) automatically match multiple, executable orders according to a priority scheme, and (iv) execute a matching algorithm that maximizes tradable volume when an executable order can not be matched according to the priority scheme. The system may be executed at a server or participant system, or combination of the two.