This paper studies the e ect of commitment based on the truth-telling-oath developed by Jacquemet, Joule, Luchini, and Shogren (2013) on tax compliance decisions. In a Baseline condition, participants play a classical tax evasion game without audits. In an Oath condition, the participants are rst o ered to sign voluntarily a truth-telling oath, before playing the same tax evasion game. Results show that in Experiment 1, compliance increases by one third under oath compared to the Baseline. Experiment 2 reproduces this result and highlights for the rst time in the literature that the oath e ect could be due to a change of taxpayers' preferences towards honest or dishonest scal declarations.

Please note that this paper is an invited paper for Claude Fluet's session.