Gavrilova, Olga; Randla, Tiina; Vallner, Leo; Starndberg, Marek; Vilu, Raivo (2005). Life Cycle Analysis of the Estonian Oil Shale Industry(PDF) (Report). Tallinn: Tallinn University of Technology. p. 34. Archived from the original(PDF) on 2013-08-25. Retrieved 2012-10-27.
Gavrilova, Olga; Randla, Tiina; Vallner, Leo; Starndberg, Marek; Vilu, Raivo (2005). Life Cycle Analysis of the Estonian Oil Shale Industry(PDF) (Report). Tallinn: Tallinn University of Technology. p. 34. Archived from the original(PDF) on 2013-08-25. Retrieved 2012-10-27.