CH2M Hill Companies 10-Q 2005 Q3 Quarterly report

Exhibit 32.1

CERTIFICATION

PURSUANT TO RULE 13A-14(B) OF THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED, AND SECTION 1350 OF CHAPTER 63 OF TITLE 18 OF THE UNITED STATES CODE (18 U.S.C.
SECTION 1350)

In connection with the Quarterly Report of CH2M HILL Companies, Ltd. (the “Company”) on Form 10-Q for the quarterly period ended September 30, 2005 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Ralph R. Peterson, Chief Executive Officer of the Company, certify, pursuant to the requirements set forth in Rule 13a-14(b) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and Section 1350 of Chapter 63 of Title 18 of the United States Code (18 U.S.C. Section 1350), that to the best of my knowledge:

(1)The Report fully complies with the requirements of section 13(a) or 15(d) of the Exchange Act; and

(2)The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/Ralph R. Peterson

Ralph R. Peterson

Chief Executive Officer

November 4, 2005

This certification “accompanies” the Report to which it relates, is not deemed filed with the SEC and is not to be incorporated by reference into any filing of the Company under the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934, as amended (whether made before or after the date of the Report), irrespective of any general incorporation language contained in such filing.  A signed original of this written statement has been provided to the Company and will be retained by the Company and furnished to the Securities and Exchange Commission or its staff upon request.