Specific Criticisms:

Minor corrections:

Page 2, first sentence of 2nd paragraph: Change “was gotten from” to “was obtained from.”

Page 2, last sentence of 2nd paragraph (and throughout): “peer-to-peer” is preferable to “peer2peer.”

Page 2, first sentence of last paragraph: Change “publications is actually” to “publications are actually.”

Page 2, last sentence of 3rd paragraph: Change “lead” to “led” (past tense).

Page 2, first sentence of Data Sources (and throughout): Change “DOI” to “DOIs” for plural use.

Page 2, second sentence of Data Sources: Change “downloads” to “download requests”

Page 2, second sentence of Resolving DOIs: Change “meta data” to “metadata.”

Page 2, second sentence of Results (and throughout): Insert comma after “i.e.”

Page 3, first sentence of “Which Journals are Being Read?” and first sentence of “Are Publishers Created Equal?”: Change “at least a single paper downloaded” to clarify that you’re referring to the 6 months included in the log dataset.

Page 3, first paragraph of the Discussion section: Change “large” to “largely.”

Page 3, first paragraph of the Discussion section: “the whole corpus of Sci-Hub” implies you used the articles themselves. Change to “metadata for the whole corpus” or something similar.

Page 3, second paragraph of the Discussion section: Change “more and more surpassed” to “more and more by.”

Page 3, last paragraph: errant comma after ‘the long tail of’.

Page 6, “Competing interests”: Change “SciHub” to “Sci-Hub.”

Reference [1] should read “Balázs Bodó” instead of “Bodó Balázs.” “Bodó” is both his legal surname and his familiar name, so he occasionally flips the order.

In general, this is a clearly written and argued paper on a developing topic affecting the scholarly communications ecosystem. The author has engaged with much of the recent literature on the topic of which we are aware. The underlying data is freely available and thus possible to replicate. The quantitative analysis proceeds logically and is easy to understand. There are a few areas where we would like to see discussion expanded (noted below) though overall this paper is a very valuable contribution to the literature on this topic.The abstract brings up the question of who uses Sci-Hub and why. However, there is relatively little discussion of this in the paper. By our reading of the literature, the question has not been rigorously addressed to date. But some have taken steps toward an answer. Specifically Travis, (2016) is a data point worth discussing < http://www.sciencemag.org/news/2016/05/survey-most-give-thumbs-pirated-papers >. (The survey had a large response rate but should be viewed with the skepticism that would normally apply to any “open” internet survey.)The Supplementary Figures are worth incorporating into the text. S2, in particular, is an informative chart. It should be improved by matching the colors for each publisher in the legend. That is, “other” should appear as the darkest blue in both bars, rather than being assigned different shades of blue as it is presently. That will allow readers to observe the important differences easily.Your methods section should include some additional discussion of what you mean by “expected number of downloads for each publisher.” You are using “expected” in a mathematical sense that diverges from the word’s everyday meaning, so you should spell this out for the reader.We find the use of the term “Black Open Access” in the discussion section puzzling. “Guerilla open access” is more widely used, as suggested by Google Trends < https://trends.google.com/trends/explore?q=%22black%20open%20access%22,%22guerilla%20open%20access%22 >. Additionally, there are important issues of “respectability politics” to consider here; there are vocal OA advocates and practitioners who condemn Sci-Hub and do not want the OA movement to be associated with it or with copyright violation. Using the word “black” may be interpreted as implying that Sci-Hub is compatible with so-called green and gold OA publishing. Librarians in particular are loath to associate Sci-Hub with the OA movement, due to professional norms that often include upholding intellectual property restrictions on ethical grounds (e.g., < http://crln.acrl.org/content/78/2/86.full >, https://thewinnower.com/papers/3489-signal-not-solution-notes-on-why-sci-hub-will-not-open-access >. On the other end of the spectrum, Sci-Hub’s supporters and sympathizers may object to negative connotations conjured by the term “black.” None of the above comments are meant to imply that your usage of “Black Open Access” is wrong. However, if you are going to use the less familiar term, you should explain why and note that this is a contested issue.In the Introduction section, your remarks on Sci-Hub’s legal status are well made, but another aspect of this is the fact that credential sharing is explicitly prohibited by many publishers (and some libraries) in their terms of use. This is worth mentioning. Elsevier’s and Wiley’s Terms are clear on this issue. < https://www.elsevier.com/legal/elsevier-website-terms-and-conditions > < http://onlinelibrary.wiley.com/termsAndConditions Due to the ambiguous legality of copying factual and educational works under various copyright regimes, we prefer the terms “potentially illegal” or “likely illegal” when describing Sci-Hub’s activities. A recent ruling in India, for instance, suggests that Sci-Hub may not violate the law in that country.Also in the Introduction, the citation for the sentence discussing #icanhazpdf refers to Cabanac, 2015. However, #icanhazpdf is mentioned in that article only in passing. A more thorough analysis can be found in Gardner & Gardner, 2015. < http://eprints.rclis.org/24847/ Bodó deserves to be cited, but there are better sources on long-term changes in the academic publishing industry. Thompson (2005) is an especially good candidate. And Royster’s slides on the history of the OA movement [3] strikes us as insufficiently authoritative. Willinsky (2006) and/or Suber (2012) are potential alternatives.Under “Data Sources,” you should credit Elbakyan (not Hahnel) with releasing the list of DOIs in Sci-Hub.---Suber, Peter. 2012. Open Access. MIT Press Essential Knowledge Series. Cambridge, Mass: MIT Press.Thompson, John B. 2005. Books in the Digital Age: The Transformation of Academic and Higher Education Publishing in Britain and the United States. Cambridge, UK ; Malden, MA: Polity Press.Willinsky, John. 2006. The Access Principle: The Case for Open Access to Research and Scholarship. Cambridge, MA: MIT Press.