In a vertical form, fill, seal machine (10) that produces liquid-filled stand-up pouches, a flat vertical seal tube (26) is surrounded by an envelope of thermoplastic film (28) that is closed along one longitudinal edge (34) and open along the opposite longitudinal edge (36). A main drive assembly (54) includes drive members (56) that press opposite sides of the envelope (28) against the flat fill tube (26). An auxiliary film drive assembly is responsive to film tension. Stand-up base cups (B) are formed seriatim along the closed longitudinal edge (34) of the envelope (28). Fitments (F) are inserted seriatim into the open longitudinal edge (34), in correspondence with respective cups (B), and are sealed to the thermoplastic film (28), first by a spot sealer and then by a top sealer.