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2. Advanced Resources International, Inc. (ARI), 2010. Retrieved on 2011-06-12. http://www.adv-res.com/pdf/Annual-Gas-Shale-Production.pdf.
3. American Enterprise Institute, (AEI) 2009. Future energy: natural gas fracking–who blew up the “bridge to the future”? Retrieved on 2011-06-12. http://221.179.130.44:83/1Q2W3E4R5T6Y7U8I9O0P1Z2X3C4V5B/www.oogeep.org/downloads/file/Publications/AEI_Fracking_Explaination%20(2).pdf
4. Hydrogen as tracer gas for leak testing. Germany;Block;ECNDT–Tu,2006
5. Recent developments of the Barnett Shale play, Fort Worth Basin;Bowker,2002