Abstract: A tensioner and method for use in holding the mouth of a bag in an open position has an annular body made of flexible and resilient material with a perimeter of fixed length. The tensioner can be compressed by manually forcing a periphery of the annular body inward. In the compressed position, the annular body is inserted into the mouth of the bag and the inward pressure is removed to allow the annular body to expand against the sides of the bag with sufficient pressure to hold the bag open and to hold the annular body in the installed position within the bag. A tensioner and bag in combination is also described.