In a packet-based transaction processing system, workload is balanced across multiple computer systems. A plurality of packets is received from a plurality of clients over a plurality of communications sessions. Each of the plurality of packets includes a portion of a transaction involving a financial transaction instrument that requires authorization. The plurality of packets are processed to assemble a plurality of transactions. Each of the plurality of transactions is then transmitted to an application server selected from a plurality of servers that provides authorization for the transactions. The server may be selected from the plurality of servers based on a round-robin distribution of the plurality of servers, and additionally, the round-robin distribution may be modified to account for a workload on each of the plurality of servers.