Pré-publication, Document de travail: Real economic commitment (or the lack of it) of others affects a person's preferences to cooperate. But what if the commitment of others cannot be observed ex ante? Herein we examine how a classic non-monetary institution– a solemn oath of honesty –creates economic commitment within the public goods game. Commitment-through-the-oath asks people to hold themselves to a higher standard of integrity. Our results suggest the oath can increase cooperation (by 33%)– but the oath does not change preferences for cooperation. Rather people react quicker and cooperate, taking less time to ponder on the strategic free riding behavior.