He subsequently wrote two other works on right-wing extremism and national socialism in Norway: Hitler eller Quisling?
Perspektiver på utviklingen av en norsk nasjonal identitet på 1800-tallet; Sørensen was the editor and wrote the opening chapter, Hegemonikamp om det norske, where he identified fourteen distinct projects of nation building in Norway between 1770 and 1945.
with Hans Fredrik Dahl, a work on the legal purge in Norway after World War II.
[7] Historien om det som ikke skjedde, published in the same year, revolves around various counterfactual history events.
[9] In 2010, he published a book on totalitarian ideologies, entitled Drømmen om det fullkomne samfunn.
[10] Sørensen is also considered an international expert on the Donald Duck universe,[11][12] and was behind the publishing of the complete, thirty-volume works of Carl Barks in Norwegian, Swedish and Danish in 2004.
[13] Sørensen's expertise also includes the world of The Phantom, and he was actively involved with the publishing of twenty volumes chronicling the different generations of Phantoms, each separate volume featuring a scholarly article, written by Sørensen, summarising the relevant historical themes.