Exhibit 13 CERTIFICATIONS UNDER SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002 ------------------------------------------------------------------ Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, each of the undersigned certifies that this periodic report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and that information contained in this periodic report fairly represents, in all material respects, the financial condition and results of operations of Nordic American Tanker Shipping Limited. /s/ Herbjorn Hansson Herbjorn Hansson Chief Executive Officer /s/ Rolf Amundsen Rolf Amundsen Chief Financial Officer Date: June 30, 2004