Open Educational Resources aim to offer learning to all, yet the language level used in resources could be a barrier to many potential learners. This paper examines the readability of 200 OER courses in English from two major OER course platforms. We compared the means of readability metrics between these OER courses at different educational levels and subject categories that the platforms offer using inferential statistics as well as cluster analyses. Results prove that there is a progression of difficulty between lower and higher educational levels with introductory courses being easier to read. However, the analysis also highlighted that more than 86% of the courses require an advanced level of English language proficiency. On the other hand, subject matter does not appear to be linked with the readability of the courses. This study contributes further to the current discussion of the inclusiveness of OER and the factors that hinder its universal use. The study addresses a gap in the literature as, to our knowledge, no other studies have analysed the linguistic accessibility of OER English learners and consideration of the meaning of the educational levels assigned to OER courses has been limited.