Open Educational Resources (OER) represent a small but growing portion of the educational resources market, but the use of OER in engineering is limited. This study seeks to identify the current adoption patterns of OER in engineering mechanics courses and barriers to adoption. Research questions are examined through the lens of Rogers' Diffusion of Innovation model. A survey of mechanics instructors across the United States, combined with publicly available data from college and university websites, were used to identify instructor practices and opinions regarding OER. During the 2017-2018 academic year, widespread OER usage was found at only a handful of institutions. However, knowledge of OER among mechanics instructors was high, and many instructors reported an interest in OER for their courses. A lack of quality OER content for engineering mechanics courses seems to be the primary barrier to more widespread adoption.