In a great variety of situations, individuals engage in behaviors which are costly for them but advantageous for their counterpart because they previously committed to do so. In many cases, such commitments are not legally binding. Vanberg shows that people tend to honor them because they have a taste to keep their word. However, he does not consider the important distinction between bilateral promises and unilateral promises. The present project explores experimentally Vanberg's motivation when it comes to Agreements as opposed to unilateral promises.