In some educational settings, the cost of textbooks approaches or even exceeds the cost of tuition. Given limited resources, it is important to better understand the impacts of free open educational resources (OER) on student outcomes. Utilizing digital resources such as OER can substantially reduce costs for students. The purpose of this study was to analyze whether the adoption of no-cost open digital textbooks significantly predicted students' completion of courses, class achievement, and enrollment intensity during and after semesters in which OER were used. This study utilized a quantitative quasi-experimental design with propensity-score matched groups to examine differences in outcomes between students that used OER and those who did not. The demographics of the initial sample of 16,727 included 4909 students in the treatment condition with a pool of 11,818 in the control condition. There were statistically significant differences between groups, with most favoring students utilizing OER.