Ill. Admin. Code tit. 44, § 2600.310
c) Competitive Sealed Proposals may be used on a case-by-case basis when it is determined by the Procurement Officer that competitive sealed bidding is either not practicable or not advantageous.
3) The key element in determining whether use of a proposal is advantageous is the need for flexibility. The competitive sealed proposal method differs from competitive sealed bidding in two important ways:
A) whether the contract needs to be other than a fixed-price type;
6) Competitive sealed proposals may be used if it is determined that it is not advantageous to the State, even though practicable, to use competitive sealed bidding. Factors to be considered in determining whether competitive sealed bidding is not advantageous include:
g) Proposal Discussions with Individual Offerors