Below is what Illinois' largest utilities charge for the gas you use to heat your home. The Purchased Gas Adjustment (PGA) is a "supply" charge that changes monthly. It's different from the companies' "delivery" charges, which you pay to get the gas to your home. See what you're paying and how it compares to other utilities.

Utility Company	May 2013 (cents/therm)	Apr. 2013 (cents/therm)	Change (cents/therm)	Percent
Ameren Zone 2 (CILCO)	60.08	56.41	3.67	6.51%
Ameren Zone 1 (CIPS)	59.87	56.21	3.66	6.51%
Ameren Zone 3 (IP)	60.20	56.52	3.68	6.51%
Ameren Zone 1 (Metro East)	59.87	56.21	3.66	6.51%
Liberty Utilities (formerly Atmos Energy)	TBP	0.00
MidAmerican Energy	TBP	59.18
NICOR	53.00	48.00	5.00	10.42%
North Shore Gas	51.38	47.17	4.21	8.93%
Peoples Gas	46.92	42.86	4.06	9.47%

Utility Company	May 2013 (cents/therm)	May 2012 (cents/therm)	Change (cents/therm)	Percent
Ameren Zone 2 (CILCO)	60.08	58.76	1.33	2.26%
Ameren Zone 1 (CIPS)	59.87	64.91	(5.05)	(7.78)%
Ameren Zone 3 (IP)	60.20	61.77	(1.56)	(2.53)%
Ameren Zone 1 (Metro East)	59.87	64.91	(5.05)	(7.78)%
Liberty Utilities (formerly Atmos Energy)	TBP	23.28
MidAmerican Energy	TBP	32.84
NICOR	53.00	22.00	31.00	140.91%
North Shore Gas	51.38	32.33	19.05	58.92%
Peoples Gas	46.92	29.14	17.78	61.02%

Utility Company	May 2013 (cents/therm)	May 2008 (cents/therm)	Change (cents/therm)	Percent
Ameren Zone 2 (CILCO)	60.08	95.33	(35.25)	(36.98)%
Ameren Zone 1 (CIPS)	59.87	88.72	(28.85)	(32.52)%
Ameren Zone 3 (IP)	60.20	101.19	(40.99)	(40.51)%
Ameren Zone 1 (Metro East)	59.87	98.15	(38.28)	(39.00)%
Liberty Utilities (formerly Atmos Energy)	TBP	107.75
MidAmerican Energy	TBP	121.25
NICOR	53.00	124.00	(71.00)	(57.26)%
North Shore Gas	51.38	110.73	(59.35)	(53.60)%
Peoples Gas	46.92	124.19	(77.27)	(62.22)%

In addition to comparing the cost per therm, the following chart includes average usage.

Month January February March April May June July August September October November December	Average Therms 250 250 150 100 25 25 25 25 25 100 150 200

Most consumers are aware that usage drops during warmer months, which is followed commonly by a drop in natural gas prices. Usage during colder months—when the price per therm can peak—may be ten times greater than during summer months. For example, average consumption in January is 250 therms, while the average in May is just 25 therms.

The following chart compares the usage from the beginning of the year to the end of the current month. It does not include additional fees or taxes.

Utility Company	In 2013	In 2012	Difference 2013-2012	Pct (%) Change
Ameren Zone 2 (CILCO)	$414.72	$462.84	$(48.12)	(10.40)%
Ameren Zone 1 (CIPS)	$440.08	$509.42	$(69.34)	(13.61)%
Ameren Zone 3 (IP)	$434.01	$439.88	$(5.88)	(1.34)%
Ameren Zone 1 (Metro East)	$440.08	$509.42	$(69.34)	(13.61)%
Liberty Utilities (formerly Atmos Energy)	$205.53	$345.85	$(140.32)	(40.57)%
MidAmerican Energy	$432.10	$382.49	$49.62	12.97%
NICOR	$329.25	$277.00	$52.25	18.86%
North Shore Gas	$351.99	$320.58	$31.41	9.80%
Peoples Gas	$318.60	$283.52	$35.07	12.37%
Average Cost	$374.04	$392.33	$(18.3)	(4.66)%

The Purchased Gas Adjustment (PGA) charge is based on the price that a utility pays for natural gas. Under the law, gas utilities are supposed to pass on this cost to customers, without a markup. The Illinois Commerce Commission (ICC) doesn't approve this per-therm charge in advance, but it reviews the charge annually and can order a refund for customers if it finds the utilities weren't using sound business practices to buy gas at a reasonable cost. Depending on the utility, this charge also is called the "cost of gas charge," the "natural gas cost," the "gas charge adjustment," or the "gas supply charge." A gas meter measures usage in cubic feet, but your utility converts that figure to a unit of measurement called a "therm" on your gas bill. An average home furnace uses about one therm per hour of heat production.

For more information read Making Sense of Your Gas Bill.