An experimental analysis of voluntary, binary contributions for step-level public goods is presented. Independent information is obtained on individual value orientation and expectations about the behaviour of other subjects using incentive compatible mechanisms. The effects of increasing payoffs for the public good and of decreasing groupsize are investigated. Attention is focused on (I) the determination of expectations; (2) the use of expectations when deciding on behaviour; (3) differences in expectations and behaviour between individuals with different value orientations.