Overall, e-books purchased in packages had a 50% use rate and an average cost per use of $3.39, e-books purchased through firm orders had a 52% use rate and an average cost per use of $22.21, and e-books purchased through demand driven acquisitions had an average cost per use of $8.88 and 13.9 average uses per title. Package purchasing was cost effective for science, technology, engineering, and mathematics (STEM) materials and medicine (MED) materials. Demand driven acquisition was a particularly good strategy for humanities and social sciences (HSS) titles.