In a binding way, members of a group pledge to contribute to action A if a total contribution level is reached (often a monetary threshold, or a quorum of "N" members making the same pledge). If the threshold level is met (perhaps by a certain expiration date), the action is taken and the public good is provided; otherwise, the parties are not bound to carry through the action and any monetary contributions are refunded. The treatment of excess contributions varies: they may be lost, rebated proportionally to the contributors, or used to provide more of the public good.