30 ILCS 500/25-15: Method of source selection.

(a) Competitive sealed bidding. Except as provided in subsection (b) and Sections 20-20, 20-25, and 20-30, all State contracts for supplies and services shall be awarded by competitive sealed bidding in accordance with Section 20-10.

(b) Other methods. The chief procurement officer may establish by rule (i) categories of purchases, including non-governmental joint purchases, that may be made without competitive sealed bidding and (ii) the most competitive alternate method of source selection that shall be used for each category of purchase.