Kristoffer Kruken - Ola Stemshaug: Norsk personnamnleksikon, Det Norske Samlaget, Oslo 1995, ISBN 82-521-4483-7
Statistisk sentralbyrå, Namnestatistikk: 14 143 males with the given name Espen living in Norway on January 1st 2011, with the frequency peak in the 1980s. Accessed on April 29th, 2011.