This study examines the indexing of open access journals in the engineering disciplines. The sample used in this study was generated from a title listing pulled from the Directory of Open Access Journals (DOAJ) in late 2013. Indexing data from four prominent commercial databases in the discipline, Compendex, Web of Science, Inspec, and Scopus, were gathered in late 2017. The four-year interval was a critical component to the methodology, in that it provided sufficient time for these open journals to establish themselves in the research marketplace and earn the attention of leading indexers. The study found that while no single database provided excellent coverage of the open access content, in aggregate, the four databases indexed journals currently listed by the DOAJ reasonably well. The study also found that the four commercial databases indexed current DOAJ content at a much higher rate than content that was no longer listed in the DOAJ.