the present invention is a disposable , presterilized bioreactor formed of molded plastic , having a top and body attached to each other . one or more ports are formed in the top , side and bottom of the housing . the one or more ports that are below the liquid / air interface level may be used as sampling ports , access ports for probes or drains or supply ports for liquids or gases . the bioreactor provides a direct retrofit for the existing glass or steel assembly that utilizes the existing support structures and controls . the molded design overcomes issues of discontinuity , dead spots and the like due to its fixed dimensions that are built in by the molding process . reproducible probe and other equipment locations are guaranteed through the use of the molded port features .