We use a sequential voluntary contribution game to compare the relative impact of a first-mover’s non-binding announcement versus binding commitment on cooperation. We find that a non-binding announcement and a binding commitment increase individual contributions to a similar extent. Since announced contributions systematically exceed commitments, in sessions with a non-binding announcement, second-movers tend to contribute more to the group activity than in sessions with a binding commitment. Yet, second-movers appear to be more motivated towards achieving a social optimum when the (...) first-mover uses commitment. We also find that a non-binding announcement has a higher impact on individual propensity to cooperate than the ex post contribution of the first-mover. However, the failure to make announced contributions decreases cooperation even though the first-mover is reassigned in every period. (shrink)