Corporate credit rating, Moody's (04.03.2011)
Corporate credit rating, Standard & Poor’s (10.02.2011)
Corporate credit rating, Standard & Poor’s (16.02.2010)
Corporate credit rating, Moody's (21.08.2008)
Corporate credit rating, Standard & Poor’s (21.07.2008)
Corporate credit rating, Moody's (25.08.2006)
Corporate credit rating, Standard & Poor’s (08.08.2006)