1. Aberdeen Group. (2007). The Spend Analysis Benchmark Report. Aberdeen Group. Retrieved from https://www.unspsc.org/Portals/3/Documents/Aberdeen_Spend_Analysis_Report.pdf
2. Aberdeen Group. (2008). The e-Procurement benchmark report. Aberdeen Group. Retrieved from http://onget.net/documents/Aberdeen_eproc_sept2008.pdf
3. APEC. (1999). Non-Binding Principles on Government Procurement: Report by the Chair of the Government Procurement Experts Group. Retrieved from http://mddb.apec.org/documents/2006/GPEG/GPEG2/06_gpeg2_005.pdf
4. The EC Procurement Directives, national procurement policies and better governance: The case for a new approach;S.Arrowsmith;European Law Review,2002
5. Arrowsmith, S. (2009). EC Regime on Public Procurement. In Thai, K. V. (Ed.), International Handbook of Public Procurement (pp. 251-289). CRC Press, Taylor and Francis Group.