Apparatus and method for controlling modeling material supply in a three-dimensional object-printing system (100). The apparatus may include one or more cartridges (180) containing modeling materials that may be connected via a set or matrix of valves (175) to the three-dimensional object printing system (100). Sensors (185) associated with the cartridges (180) may continuously or periodically monitor the status of the material within the cartridges. The controller receives data about the material presently available in each cartridge (180) and computes supply parameters for the available materials in the various cartridges (180).