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Illinois: Build an auditable result instead of a sales story
Start with EIA: natural gas volume, heat content and energy units. The table below links this decision to the represented gas companies in Illinois. It does not establish service or supplier availability for every account.
Define the counterfactual
Retain what the business would otherwise have paid for the same service months and quantities. Identify whether that is an existing contract, an effective utility supply component or another dated written offer. Do not switch baselines after seeing the result.
Bridge model to invoices
Separate quantity changes from comparable price changes, then reconcile fixed charges, retained delivery and timing corrections. Preserve enrollment confirmation and invoices before presenting an actual outcome. A favorable calculator scenario is only a model.
Illinois utility application
| Gas service company | Evidence needed for the baseline | Primary reference |
|---|---|---|
| Nicor Gas | Utility supply benchmark versus AGS supply and recurring fees, keeping delivery separate | Official program / tariff |
| Ameren Illinois | Applicable utility gas supply and delivery components; incremental transport costs if eligible | Official program / tariff |
| Peoples Gas | Utility supply benchmark versus AGS supply and recurring fees, keeping delivery separate | Official program / tariff |
| North Shore Gas | Utility supply benchmark versus AGS supply and recurring fees, keeping delivery separate | Official program / tariff |
| MidAmerican Energy | State-specific gas supply and delivery components | Official program / tariff |
Nicor Gas: the program detail behind this decision
The ICC identifies Nicor Gas, Peoples Gas and North Shore Gas for residential and small-commercial Gas Choice. An Alternative Gas Supplier sells supply while the delivery utility remains. The ICC’s utility list does not establish that every supplier accepts every commercial class or offers a suitable contract. Program Illinois.
Apply the evidence to an account file
The case file needs comparable evidence for Utility supply benchmark versus AGS supply and recurring fees, keeping delivery separate. First establish The named delivery company and its eligible small-commercial service class so the proposed baseline is an available alternative for this account.
Worked case: distinguish a model from an observed result
For a hypothetical 10,000-therm account, $0.80 per therm plus $20 monthly models to $8,240. An alternative at $0.76 plus $60 monthly models to $8,320. That is an $80 increase in the defined supply scope, not a saving. This conclusion is still only a scenario until eligibility, accepted enrollment and actual comparable invoices are established. Keep the same quantity and delivery period in both calculations. Do not present these invented inputs as a local client case or publish them as market rates.
Turn the review into a calculation
Compare constant supply rates and fees. Enter documented assumptions in matching energy units. Keep any charge outside both supply offers separate; the result does not establish eligibility or an available quote.
Read the Illinois utility guide for the wider service-company distinctions. Convert billed gas units using the bill’s heat-content factor when moving from volume to energy.
Sources and review notes
- EIA: natural gas volume, heat content and energy units
- Illinois ICC Natural Gas Choice FAQ
- Midamerican Territory
Reviewed October 16, 2026. Program information can change. Confirm the effective utility tariff, supplier availability and written offer before proceeding. Examples and planning tools are educational; they are not executable quotes or verified customer results.