Many companies offer their customers voluntary carbon ‘offset’ certificates to compensate for greenhouse gas emissions. Voluntary offset certificates are cheap because the demand for them is low, allowing consumers to compensate for their emissions without significant sacrifices. Regarding the distribution of emission reduction responsibilities I argue that excess emissions are permissible if they are offset properly. However, if individuals buy offsets only because they are cheap, they fail to be robustly motivated to choose a permissible course of action. This suspected lack of robust motivation raises both pragmatic questions about the functioning of offsetting schemes and moral questions about the worth of such unstable motives. The analysis provided here also has wider implications for the normative analysis of partial compliance and ‘many hands’ problems, especially for those cases where compliance levels and costs interact.