`  ::: I would prefer keeping it as an individual book, since none of the 3 parts considered individually can be seen a ``closed story``, unlike e.g. the individual Harry Potter books. But I agree this can be disputed. @: The reference for the LotR 150 million figure (see link in the article) says: ``Fully one-third of the 150 million copies of The Lord of the Rings sold to date were purchased after the release of the first film in the series.`` To me this implies 150 million copies of the whole story, i.e. 150 million of each of the 3 parts (if we neglect the one-volume editions). So if we considered LotR a 3-part series, we would get a number of about 450 million copies, putting it on top position, even above the Harry Potter series.  `