EXHIBIT 3.1 CERTIFICATE OF LIMITED PARTNERSHIP OF EQUISTAR CHEMICALS, LP This Certificate of Limited Partnership of Equistar Chemicals, LP (the "Partnership") is being executed and filed by the undersigned, the two general partners of the Partnership (the "General Partners"), to form a limited partnership under the Delaware Revised Uniform Limited Partnership Act. 1. The name of the limited partnership is Equistar Chemicals, LP. 2. The address of the registered office of the Partnership in the State of Delaware is Corporation Trust Center, 1209 Orange Street, Wilmington, New Castle County, Delaware 19801, and the name and address of the registered agent for service of process on the Partnership in the State of Delaware is The Corporation Trust Company, Corporation Trust Center, 1209 Orange Street, Wilmington, New Castle County, Delaware 19801. 3. The name and business address of each of the General Partners is: Lyondell Petrochemical G.P. Inc. 1221 McKinney Suite 1600 Houston, Texas 77010 Millennium Petrochemicals GP LLC Meadowood Shopping Center 2664 Capitol Trail Newark, Delaware 19711 -1- IN WITNESS WHEREOF, each of the undersigned has hereunto set its hand this 17th day of October, 1997. Lyondell Petrochemical G.P. Inc. By: /s/ Jeffrey R. Pendergraft --------------------------------------- Name: Jeffrey R. Pendergraft ----------------------------------- Title: Executive Vice President ---------------------------------- Millennium Petrochemicals GP LLC By: /s/ George H. Hempstead --------------------------------------- Name: George H. Hempstead ----------------------------------- Title: Senior Vice President ---------------------------------- -2-