• Hydrogenation of Estonian oil shale and shale oilKogerman, Paul; Kopvillem, Jaan1932 https://www.ester.ee/record=b2170142*est https://digikogu.taltech.ee/et/Item/b761323c-f805-4666-bdd7-3a32f1072514
• Hydrogenation of Estonian Oil Shale and Shale OilKogerman, Paul; Kopvillem, JaanThe Journal of the Institution of Petroleum Technologists1932 / p. 833-845 : ill https://www.ester.ee/record=b2557232*est