Koetschau, Klostermann, Baehrens. Origenes Werke [GCS Ed.]. 1899-19.
The Internet Archive project is digitizing big lots of the GCS series, as alone volumes or specific series/opera omnia.
The works of Origen [the first 7 volumes of Origenes Werke] are now available for the use and consult by the community, and we hope that some other authors will be digitized and added to this great service.
Please note the whole collection -as indexed by Worldcat.org-, include at least 12 titles.
You can find all the available volumes in Archive.org.
Or you can browse and preview all of them in our Bibliotheca Pretiosa.