Abstract: An automatic bag tying apparatus for converting an open bag loosely holding a substance into a tight package. A first gripping assembly tightly grips the unsealed bag toward its mouth. A second gripping assembly loosely and slidably grips the unsealed bag to form a neck. A displacement assembly displaces the gripping means relative to each other to cause the gripping means to move apart until the substance stops against the second gripping means. Bag closure applying apparatus then applies a closure to the bag in close proximity to the substance to create the final, closed, tight package. The tying apparatus further includes a guide assembly, and the gripping assemblies open sufficiently wide to allow passage of the bag and product therethrough which enables gravity loading of the apparatus. Tightening of the bag about the product is also controlled by pressure sensing apparatus to prevent over-tensioning of the bag.