Commercial Natural Gas in Illinois: Suppliers, Rates & Utilities

Commercial natural gas in Illinois works much like electricity: an eligible business can buy the gas supply from a competitive supplier while the utility continues to deliver it — but the gas utility, and even whether supplier choice exists, depends on where the facility sits. This page maps the territories and explains what a real gas quote requires.

Who this is for

Businesses with meaningful heating, process, or hot-water gas load — manufacturers, food service and processing, hotels and multifamily, laundromats, and any facility where therms are a real line item. It is written for the people who sign the contract: facilities, operations, and finance.

Know your gas utility first

Unlike electricity (two dominant delivery utilities), Illinois gas is split across several:

• Peoples Gas — the City of Chicago only.
• Nicor Gas — much of northern Illinois outside Chicago (600+ communities).
• North Shore Gas — a narrower set of Lake County and far-north communities from roughly Winnetka to the Wisconsin line (Waukegan is on North Shore Gas, not Nicor).
• Ameren Illinois — much of central and southern Illinois.

Some communities straddle a boundary — Buffalo Grove, for instance, has areas served by both Nicor and North Shore Gas — so the only reliable answer for a specific address is the utility name printed on a recent bill.

Where supplier choice exists — and where it works differently

In Nicor, Peoples, and North Shore territory, eligible commercial customers can contract with a licensed alternative gas supplier while the utility delivers the gas and handles safety and emergencies. In Ameren Illinois gas territory the model is different: there is no standard small-commercial supplier-choice program, and only larger non-residential customers can self-supply through Ameren's Rider T transportation service. On this site we do not describe a "switch your gas supplier" path where it does not exist.

Supply vs. delivery for gas

The supply charge is the commodity — often quoted per therm, and on utility service tied to a purchased-gas cost that adjusts over time. The delivery charge covers the utility's distribution system, metering, and applicable riders and taxes. A supplier contract prices the supply portion; delivery stays with the utility under its tariff. As with electricity, don't apply a supply-price difference to the whole bill.

On the default utility service, the commodity portion is generally a pass-through: the utility buys gas and recovers what it paid through a periodically adjusted purchased-gas charge, without a markup on the commodity itself. That is why utility gas supply moves with the market from period to period rather than staying flat. A competitive supplier's offer replaces that moving commodity charge with the supplier's own price and terms — which is where a fixed term can add budget certainty, and where the contract language deserves a close read.

Anatomy of a commercial gas bill

Reading a gas bill in groups keeps comparisons honest:

1. Account and meter — service address, account number, rate class, billing period days, and the delivery utility. This tells you which market and rules apply.
2. Usage — therms (or, on some meters, hundred cubic feet converted to therms) for the period, and ideally the same figure for the prior twelve months.
3. Supply / commodity — the per-therm commodity charge, whether from the utility's purchased-gas cost or a supplier contract.
4. Delivery and other — customer charge, distribution charges, applicable riders, and taxes, which stay with the utility.

Only the third group is what a supplier contract prices. A common error is to compare a supplier's per-therm number against the entire bill divided by therms — that blends delivery into the comparison and overstates any difference. Compare supply to supply.

What drives a commercial gas price

• Therm usage and seasonality — most commercial gas load is heavily winter-weighted, which shapes how a term is priced.
• Load profile and interruptible/transportation status — larger accounts may qualify for transportation service with different economics.
• Contract term, start month, and market timing.
• Applicable taxes and utility riders.

Because gas is seasonal, when a term starts matters. A twelve-month term beginning in autumn covers a full heating season under one price; one beginning in spring front-loads the low-usage months and pushes the winter peak toward the back of the term. Neither is automatically better — but the start month changes how much of the contract volume falls in the expensive months, and that belongs in the decision.

How to decide: fixed, index, or staying put

There is no single right structure. The question is how much month-to-month variability the account can absorb against how much certainty it needs.

• A fixed term locks the commodity price for the contract length, which helps a budget-driven operation plan around a known number — provided the exclusions and pass-throughs in the contract are understood, not just the headline per-therm figure.
• An index or variable structure tracks the market, which can move either direction and suits an account that would rather ride the market than commit.
• Staying on utility default supply is a legitimate choice, especially where the account is small or where the utility's purchased-gas cost is the simpler benchmark to manage. Choice is an option, not an obligation.

Whatever the structure, read the contract terms — tolerance around expected volume, change-in-law pass-throughs, termination, and above all the renewal and holdover language — the same way you would on an electricity agreement. See the contract review page for the clauses that move cost.

What to watch for

• Boundary addresses. Some communities are split between utilities (Buffalo Grove has both Nicor and North Shore Gas areas), so never assume the utility from the town name — read it off the bill.
• Ameren gas is different. There is no standard small-commercial supplier-choice program in Ameren gas territory; only larger non-residential accounts can self-supply through Rider T transportation. Treat any pitch to "switch your gas supplier" downstate with skepticism.
• Comparing a winter bill to a summer quote. Seasonality makes single-month comparisons misleading. Use a full year of therms.
• Confidential account data. A utility bill carries the account number and service details; share it only through the secure request, never by posting it publicly.

What a commercial gas quote requires

A recent bill and account number, the service address and gas utility, at least twelve months of therm usage (to capture the seasonal shape), and the current contract's end date. For larger or transportation-eligible accounts, the utility rate class and any interruptible terms matter. Start with the Chicagoland natural gas procurement guide and the overview of how commercial gas choice works in Illinois, then request pricing with the documents in hand. As with electricity, no savings figure is promised in advance — the value is a correctly scoped, apples-to-apples comparison for the actual account.