A growing body of research documents the positive outcomes of research experiences for undergraduates, including increased persistence in science. Study of undergraduate lab learning experiences has demonstrated that the design of the experience influences the extent to which students report ownership of the project and that project ownership is one of the psychosocial factors involved in student retention in the sciences. To date, methods for measuring project ownership have not been suitable for the collection of larger data sets. The current study aims to rectify this by developing, presenting, and evaluating a new instrument for measuring project ownership. Eighteen scaled items were generated based on prior research and theory related to project ownership and combined with 30 items shown to measure respondents' emotions about an experience, resulting in the Project Ownership survey (POS). The POS was analyzed to determine its dimensionality, reliability, and validity. The POS had a coefficient alpha of 0.92 and thus has high internal consistency. Known-groups validity was analyzed through the ability of the instrument to differentiate between students who studied in traditional versus research-based laboratory courses. The POS scales as differentiated between the groups and findings paralleled previous results in relation to the characteristics of project ownership.