30 ILCS 500/20-5

Unless otherwise authorized by law, all State contracts shall be awarded by competitive sealed bidding, in accordance with Section 20-10, except as provided in Sections 20-15, 20-20, 20-25, 20-30, 20-35, 30-15, and 40-20. The chief procurement officers appointed pursuant to Section 10-20 may determine the method of solicitation and contract for all procurements pursuant to this Code.