A contract consists of an offer, acceptance of that offer, and consideration exchanged by parties. In Oregon, consideration is the accrual of some benefit or legal right to one party and some benefit or forbearance by the other party. What this means is that generally both sides to an agreement have to give up something (money, property, labor, etc.) in order for a contract to be valid.
However, in the recent case Compton v. Compton the Court of Appeals indicates that where a written agreement regarding the support of a child is concerned and where one of the parties relies on that agreement, the agreement may be enforceable despite the lack of consideration by the other party. The reliance on the agreement makes it enforceable. This only applies to agreements reached privately between parties without court approval.
An agreement that might run afoul of this new interpretation would consist of a written agreement for one party to provide monetary support for a child while receiving in return something that the party is already legally entitled to receive, such as visitation with the child. The best thing to do if contemplating such an agreement would be to contact an attorney.