Provided are methods for fabricating fluid separation devices with precisely-sized, shaped microscopic capillaries that can separate one immiscible fluid from another on the basis of different separation characteristics. In particular, the method comprises the steps of fabricating a first set of capillaries having a first separation characteristic and a second set of capillaries having a second separation characteristic, incorporating one end of all of the capillaries into an inlet face, incorporating the second end of the first set of capillaries into a first outlet face, and incorporating the second end of the second set of capillaries into a second outlet face. Preferably, the first set of capillaries is hydrophillic and the second set of capillaries is hydrophobic.