en: See Eurogas, Statistical Report 2012, p. 1 (http://www.eurogas.org/uploaded/Statistical%20-Report%202012_final_211112.pdf).
el: Βλ. Eurogas, Στατιστική Έκθεση 2012, σ. 1 (http://www.eurogas.org/uploaded/Statistical%20-Report%202012_final_211112.pdf).