1. Directive 2009/28/EC of the European parliament and of the council of 23 April 2009 on the promotion of the use of energy from renewable sources.
2. Natural Gas – Calculation of Calorific Values, Density, Relative Density and Wobbe Index from Composition;ISO 6976,1995
3. Natural Gas – Determination of Composition and Associated Uncertainty by Gas Chromatography, Part 1: General Guidelines and Calculation of Composition;ISO 6974–1,2012
4. Natural Gas – Determination of Composition and Associated Uncertainty by Gas Chromatography, Part 2: Uncertainty Calculations;ISO 6974–2,2012
5. http://www.biogas-renewable-energy.info/biogas_composition.html, 2014-07-23.