See the above address for the links.
Archive.org now has the first fourteen volumes of The Oxyrhynchus Papyri online in toto and in a variety of formats, for viewing and for download; Volumes 1-5 are digitized by Google Books from Harvard University Library and so should appear also on Google Books in due course. They do not yet have my favourite format, the flip book, but no doubt that will appear in due course. Volumes 6-14 are digitized by Brigham Young University and include the flip book format. I have also noted below an alternative (and superior) version of Volume 4, from University of California Libraries, which has been online for much longer.