A membrane contactor includes a housing, a stack of membrane mats, and a cap. The housing has a closed end and an open end. The closed end includes an outlet port. The cap is united to the open end and includes an inlet port. A stack of membrane mats is within the housing stacked substantially perpendicular to the longitudinal axis of the housing. Each membrane mat has a plurality of hollow fiber members. A potting material bonds the membrane mats to each other and simultaneously bonds one end of the stack to the closed end and bonds the other end of the stack to the cap. The potting material forms an internal chamber and at least one external chamber within the housing. The hollow fiber members extend through the potting material from the internal chamber into the external chambers. The inlet port and the outlet port are in communication with the internal chamber. At least one side port is in communication with the external chambers.