This study is concerned with the factors affecting user commitment towards an information system, and specifically explores reasons to use crowd-sourcing systems such as Amazon's Mechanical Turk. The first research objective is to integrate two frameworks of user commitment into one unified framework, resolving differences in terminology and bringing the different bases of commitment into line. The findings demonstrate that, although five bases of commitment have been identified in theory, only four bases can be distinctively identified through empirical research. These bases are internalisation, affection, compliance, and calculation. The second objective is to understand which of the bases of commitment in this unified framework are most material in understanding behavioural intention to use an information system. The findings highlight the importance of perceived sacrifices of non-use (calculative commitment). This study is among the first studies to use Amazon's Mechanical Turk crowd-sourcing platform in information systems research, and offers an additional methodological contribution by developing a procedure to detect Mechanical Turk respondents that do not take crowd-sourcing tasks seriously.