Business electricity and natural gas suppliers in Illinois
How commercial and industrial companies in Illinois buy electricity and gas: which utilities deliver it, what happens if you do not choose a supplier, how PJM sets the costs behind the price, and how to run a competitive purchase.
Commercial and industrial customers in ComEd and Ameren Illinois territory can buy supply from a licensed alternative retail electric supplier (ARES). Illinois straddles two grids: ComEd in northern Illinois is in PJM, Ameren Illinois in central and southern Illinois is in MISO, so capacity costs and contract terms differ across the state. Discovery Energy Utility Audits buys electricity and natural gas for multi-site companies with sites in Illinois: it inventories every account, invites every active supplier to one RFP, compares offers line for line, tracks each contract to renewal in TaraBase and audits the utility bills behind it. Its procurement fee is disclosed in advance.
01 / 07
Who delivers electricity in Illinois
The utility in each territory owns the wires and bills delivery under a tariff the Illinois Commerce Commission (ICC) approves, whoever supplies the energy. Municipal utilities and cooperatives usually sit outside retail choice. Every utility in the state is listed in Discovery's Illinois electric utility directory.
| Utility | Area | Grid |
|---|---|---|
| ComEd (Commonwealth Edison) | Chicago and northern Illinois | PJM (ComEd zone) |
| Ameren Illinois | Central and southern Illinois | MISO (Zone 4) |
| MidAmerican Energy (Illinois service area) | Quad Cities area | MISO |
02 / 07
What happens if a business does not choose a supplier
Illinois has declared supply service competitive for larger non-residential customers. In ComEd's territory, only residential customers and non-residential customers below 100 kW are eligible for the utility's blended fixed-price service; larger customers who do not choose a supplier take hourly-priced default supply passed through at wholesale cost. Discovery's briefing on Illinois capacity charges and ComEd explains why cutting consumption did not lower many bills.
03 / 07
Capacity, transmission and why prices moved
ComEd customers pay PJM capacity: Capacity is bought in a forward auction and charged to each account through its peak load contribution (PLC), set from the account's demand in the five summer peak hours of the year before. The auction price was $28.92 per MW-day for 2024/25, $329.17 for 2026/27, $333.44 for 2027/28 and $325 for 2028/29, the third auction in a row at the price cap. At $329.17 per MW-day, each 1 MW of PLC costs about $120,147 a year before the utility's adjustment factors. PJM's simulation of the 2028/29 auction without the price cap showed the ComEd zone clearing higher than the rest of the region. Ameren Illinois customers pay MISO capacity instead: MISO's 2026/27 auction set annualized prices of $116 to $126 per MW-day, down from about $212 to $217 the year before, with the summer season still at $424.30 per MW-day.
How a contract treats these charges, fixed or passed through, matters more than the headline rate. See charges by market and what to do about PJM capacity charges.
04 / 07
Natural gas for businesses in Illinois
Nicor Gas (Customer Select), Peoples Gas and North Shore Gas (Choices For You) and Ameren Illinois offer gas supplier choice, and larger sites can buy gas under transportation service. Chicago's winter peak makes firm versus interruptible a real decision; see Discovery's outlooks for Chicago (Peoples Gas) and the Chicago suburbs (Nicor Gas).
Discovery's natural gas procurement page explains transport eligibility, NYMEX and basis, balancing, and firm versus interruptible service.
05 / 07
Brokers, suppliers and licensing in Illinois
Illinois requires agents, brokers and consultants who sell or arrange retail electricity to hold an ABC license from the ICC. Ask any broker for its license. Discovery Energy acts as an energy broker in its procurement work; its energy broker licenses and registrations are held by Energy Auction Exchange, LLC. Ask Discovery for the license or registration that covers your Illinois sites. Suppliers serving Illinois customers are licensed by the Illinois Commerce Commission (ICC), which keeps the list of active suppliers. A broker can only bid your Illinois sites to suppliers active in each utility territory, and only if it is licensed or registered where the state requires it. How brokers are paid, and what to ask, is covered in energy broker fees.
06 / 07
How Discovery buys electricity and gas in Illinois
Inventory
Every Illinois account: utility, rate class, default or supplier service, contract end date, usage, capacity and transmission tags.
Check the bills
Rate class, riders, demand and meter setup are tested against the tariff before a contract locks in the baseline. See utility bill audits.
Time and bid
One RFP to every active supplier, timed with the monthly Energy Risk Report, with Illinois sites bid alongside the rest of the portfolio. See the multi-state RFP.
Compare and sign
Offers side by side on the same terms, in each structure that fits: fixed, fixed with pass-throughs, index, block and index or layered. No contract is signed without your written approval.
Track
Every contract in TaraBase, with renewals flagged well in advance so nothing rolls onto default or month-to-month pricing.
How far back utility overcharges can be refunded in Illinois is on the Illinois refunds page.
07 / 07
Questions about buying energy in Illinois
Can businesses choose their electricity supplier in Illinois?
Commercial and industrial customers in ComEd and Ameren Illinois territory can buy supply from a licensed alternative retail electric supplier (ARES). Illinois straddles two grids: ComEd in northern Illinois is in PJM, Ameren Illinois in central and southern Illinois is in MISO, so capacity costs and contract terms differ across the state.
Who are the retail energy providers in Illinois?
Suppliers are licensed by the Illinois Commerce Commission (ICC), which keeps the list of active suppliers. Discovery invites every supplier active in each utility territory to its RFPs rather than a short list.
Which electric companies serve businesses in Illinois?
ComEd (Commonwealth Edison); Ameren Illinois; MidAmerican Energy (Illinois service area). They deliver the power; the supply can come from a competitive supplier.
How do I compare commercial electricity offers in Illinois?
Put every offer on the same product, term and treatment of capacity, transmission and other pass-through charges, then compare price. Check usage tolerance, auto-renewal and early termination terms before signing.
Sources
- Illinois Power Agency, ComEd load forecast submittal (August 2025), only residential and non-residential customers below 100 kW are eligible for blended service.
- American Public Power Association, MISO 2026 Planning Resource Auction, annualized $116.06 to $126.19 per MW-day.
- Enel North America, PJM 2028/2029 auction results, uncapped simulation higher in the ComEd zone.
- PJM, 2026/2027 Base Residual Auction Report, $28.92 per MW-day for 2024/25 and $329.17 for 2026/27.
- PJM, 2028/2029 Base Residual Auction results (July 14, 2026), $325 per MW-day cap; 2027/28 at $333.44.
Find out what your bills should have cost.
Send one recent bill per site, or a list of accounts. We tell you where we expect findings before you sign anything. No upfront audit fee.