Ameren Illinois (AILLM) 8-K Unaudited Pro Forma Condensed Combined Financial Statements

Exhibit 99.1

UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS

On October 1, 2010, Central Illinois Public Service Company (“CIPS”), Central Illinois Light Company (“CILCO”) and Illinois Power Company (“IP”) completed the previously announced merger whereby CILCO and IP merged with and into CIPS, with CIPS as the surviving entity (the “Merger”), pursuant to the terms of the agreement and plan of merger (the “Agreement”), dated as of April 13, 2010, among CIPS, CILCO and IP. Upon consummation of the Merger, CIPS’ name was changed to “Ameren Illinois Company” (“Ameren Illinois”) and the separate legal existence of CILCO and IP terminated. Prior to the Merger, each of CIPS, CILCO and IP was a registrant subsidiary of Ameren Corporation (“Ameren”). Immediately following the Merger, Ameren Illinois distributed all of its shares of AmerenEnergy Resources Generating Company (“AERG”) common stock to Ameren (sometimes referred to as the “AERG distribution”) with the subsequent contribution by Ameren of AERG stock to Ameren Energy Resources Company.

The following unaudited pro forma condensed combined balance sheet and statements of income presented below are based on the historical financial statements of CIPS, CILCO and IP after giving effect to the Merger of CILCO and IP with and into CIPS and the AERG distribution. The Merger and the AERG distribution represent transactions between entities under common control. In accordance with authoritative accounting guidance, assets and liabilities transferred between entities under common control are accounted for at the historical cost basis of the common parent. The unaudited pro forma condensed combined balance sheet as of June 30, 2010, gives effect to the Merger and the AERG distribution as if these events had occurred on June 30, 2010. The unaudited pro forma condensed combined statements of income for each of the years ended December 31, 2009, 2008, and 2007, and for the interim periods for the six months ended June 30, 2010, and 2009, give effect to the Merger and the AERG distribution as if these events had occurred on January 1, 2007. The unaudited pro forma condensed combined balance sheet and statements of income are for illustrative purposes only. They should not be considered indicative of actual results that would have been achieved had the Merger and the AERG distribution actually been consummated on the dates indicated and do not purport to be indicative of results of operations as of any future date or for any future period.

The unaudited pro forma condensed combined balance sheet and statements of income reflect the following actions that occurred prior to the effective time of the Merger: (i) Ameren contributed to the capital of IP, without the payment of any consideration, all of the IP preferred stock owned by Ameren; (ii) CILCO redeemed all of its outstanding preferred stock; and (iii) CIPS redeemed all of its 7.61% first mortgage bonds. Each series of outstanding debt of CIPS, CILCO and IP, except as described above, remains outstanding and governed by the indenture under which it was originally issued, except that Ameren Illinois has been substituted as the obligor under the indebtedness of CILCO and IP.

The unaudited pro forma condensed combined balance sheet and statements of income have been derived from and should be read in conjunction with:

• CIPS’, CILCO’s, and IP’s historical unaudited financial statements and related notes as of and for the six months ended June 30, 2010 and 2009; and

• CIPS’, CILCO’s, and IP’s historical audited financial statements and related notes as of and for the years ended December 31, 2009, 2008, and 2007.

AMEREN ILLINOIS COMPANY

UNAUDITED PRO FORMA CONDENSED COMBINED BALANCE SHEET

AS OF JUNE 30, 2010

(In millions)

							Pro Forma
							Capital Structure Adjustments (a)			Push Down Effects of Purchase Accounting			Elimination  of Intercompany Balances			Distribution of AERG (g)			Ameren Illinois Company, Post-Distribution
	Historical
	CIPS		IP		CILCO
ASSETS
Current Assets:
Cash and cash equivalents	$	113	$	142	$	128	$	(62	)	$	—		$	—		$	—		$	321
Accounts receivable, net		62		174		95		—			—			(14	) (f)		(53	)		264
Other current assets		195		330		183		—			—			—			(51	)		657
Total current assets		370		646		406		(62	)		—			(14	)		(104	)		1,242
Property and Plant, Net		1,255		2,478		1,771		—			(9	) (b)		—			(975	)		4,520
Investments and Other Assets:
Goodwill		—		214		—		—			197	(c)		—			—			411
Regulatory assets		228		486		163		—			—			—			—			877
Other assets		109		68		29		—			—			—			(6	)		200
Total investments and other assets		337		768		192		—			197			—			(6	)		1,488
TOTAL ASSETS	$	1,962	$	3,892	$	2,369	$	(62	)	$	188		$	(14	)	$	(1,085	)	$	7,250
LIABILITIES AND STOCKHOLDERS’ EQUITY
Current Liabilities:
Accounts and wages payable	$	88	$	168	$	79	$	—		$	—		$	(14	) (f)	$	(18	)	$	303
Other current liabilities		316		284		371		—			—			—			(256	)		715
Total current liabilities		404		452		450		—			—			(14	)		(274	)		1,018
Long-term Debt, Net		271		1,147		279		(40	)		—			—			—			1,657
Other Deferred Credits and Other Liabilities		707		837		763		—			(3	) (d)		—			(237	)		2,067
Stockholders’ Equity:
Common stock, no par value		—		—		—		—			—			—			—			—
Other paid-in capital		257		1,349		480		33			173	(b)(c)(d)(e)		—			(310	)		1,982
Preferred stock not subject to mandatory redemption		50		46		19		(53	)		—			—			—			62
Retained earnings		273		58		376		(2	)		—			—			(262	)		443
Accumulated other comprehensive income		—		3		2		—			18	(e)		—			(2	)		21
Total stockholders’ equity		580		1,456		877		(22	)		191			—			(574	)		2,508
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$	1,962	$	3,892	$	2,369	$	(62	)	$	188		$	(14	)	$	(1,085	)	$	7,250

The accompanying notes are an integral part of these unaudited pro forma condensed combined financial statements.

AMEREN ILLINOIS COMPANY

UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF INCOME

FOR THE YEAR ENDED DECEMBER 31, 2009

(In millions)

								Pro Forma
								Capital Structure Adjustments (a)			Push Down of Effects of Purchase Accounting			Elimination  of Intercompany Transactions			Distribution of AERG (e)			Other Adjustments			Ameren Illinois Company, Post-Distribution
	Historical
	CIPS		IP		CILCO
Operating Revenues:
Electric	$	642	$	992	$	729		$	—		$	—		$	(3	) (d)	$	(427	)	$	1	(f)	$	1,934
Gas		224		501		277			—			—			(1	) (d)		—			—			1,001
Other		3		11		76			—			—			(86	) (d)		—			—			4
Total operating revenues		869		1,504		1,082			—			—			(90	)		(427	)		1			2,939
Operating Expenses:
Fuel and purchased power		372		509		284			—			—			(1	) (d)		(116	)		—			1,048
Gas purchased for resale		143		310		189			—			—			—			—			—			642
Other operations and maintenance		181		275		260			—			(6	) (b)		(89	) (d)		(76	)		1	(f)		546
Depreciation and amortization		68		116		70			—			—			—			(38	)		—			216
Taxes other than income taxes		37		64		27			—			—			—			(3	)		—			125
Total operating expenses		801		1,274		830			—			(6	)		(90	)		(233	)		1			2,577
Operating Income		68		230		252			—			6			—			(194	)		—			362
Other Income (Expenses)		6		—		(4	)		—			—			—			—			—			2
Interest Charges		29		98		41			(3	)		—			—			(16	)		—			149
Income Before Income Taxes		45		132		207			3			6			—			(178	)		—			215
Income Taxes		16		53		72			1			2	(c)		—			(64	)		—			80
Income from Continuing Operations		29		79		135			2			4			—			(114	)		—			135
Preferred Stock Dividends		3		2		1			(3	)		—			—			—			—			3
Income from Continuing Operations Available to Common Stockholder	$	26	$	77	$	134		$	5		$	4		$	—		$	(114	)	$	—		$	132

The accompanying notes are an integral part of these unaudited pro forma condensed combined financial statements.

AMEREN ILLINOIS COMPANY

UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF INCOME

FOR THE YEAR ENDED DECEMBER 31, 2008

(In millions)

								Pro Forma
								Capital Structure Adjustments (a)			Push Down of Effects of Purchase Accounting			Elimination  of Intercompany Transactions			Distribution of AERG (e)			Other Adjustments			Ameren Illinois Company, Post-Distribution
	Historical
	CIPS		IP		CILCO
Operating Revenues:
Electric	$	720	$	1,071	$	771		$	—		$	—		$	(1	) (d)	$	(342	)	$	3	(f)	$	2,222
Gas		259		620		375			—			—			—			—			1	(f)		1,255
Other		3		5		1			—			—			(8	) (d)		—			—			1
Total operating revenues		982		1,696		1,147			—			—			(9	)		(342	)		4			3,478
Operating Expenses:
Fuel and purchased power		461		654		412			—			—			—			(123	)		1	(f)		1,405
Gas purchased for resale		179		452		284			—			—			(1	) (d)		—			—			914
Other operations and maintenance		196		318		217			—			(4	) (b)		(7	) (d)		(99	)		2	(f)		623
Depreciation and amortization		67		102		77			—			—			—			(27	)		—			219
Taxes other than income taxes		37		67		25			—			—			—			(3	)		—			126
Total operating expenses		940		1,593		1,015			—			(4	)		(8	)		(252	)		3			3,287
Operating Income		42		103		132			—			4			(1	)		(90	)		1			191
Other Income (Expenses)		8		6		(3	)		—			—			1	(d)		—			(1	) (f)		11
Interest Charges		30		99		21			(3	)		—			—			(5	)		—			142
Income Before Income Taxes		20		10		108			3			4			—			(85	)		—			60
Income Taxes		5		5		39			1			2	(c)		—			(33	)		—			19
Income from Continuing Operations		15		5		69			2			2			—			(52	)		—			41
Preferred Stock Dividends		3		2		1			(3	)		—			—			—			—			3
Income from Continuing Operations Available to Common Stockholder	$	12	$	3	$	68		$	5		$	2		$	—		$	(52	)	$	—		$	38

The accompanying notes are an integral part of these unaudited pro forma condensed combined financial statements.

AMEREN ILLINOIS COMPANY

UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF INCOME

FOR THE YEAR ENDED DECEMBER 31, 2007

(In millions)

								Pro Forma
								Capital Structure Adjustments (a)			Push Down of Effects of Purchase Accounting			Elimination  of Intercompany Transactions			Distribution of AERG (e)			Other Adjustments			Ameren Illinois Company, Post- Distribution
	Historical
	CIPS		IP		CILCO
Operating Revenues:
Electric	$	772	$	1,104	$	681		$	—		$	—		$	(1	) (d)	$	(283	)	$	3	(f)	$	2,276
Gas		230		540		329			—			—			—			—			2	(f)		1,101
Other		3		2		1			—			—			(3	) (d)		—			—			3
Total operating revenues		1,005		1,646		1,011			—			—			(4	)		(283	)		5			3,380
Operating Expenses:
Fuel and purchased power		527		714		351			—			—			1	(d)		(78	)		2	(f)		1,517
Gas purchased for resale		157		390		237			—			—			—			—			—			784
Other operations and maintenance		172		271		184			—			(4	) (b)		(4	) (d)		(74	)		2	(f)		547
Depreciation and amortization		66		96		73			—			—			—			(18	)		—			217
Taxes other than income taxes		34		66		23			—			—			—			(3	)		—			120
Total operating expenses		956		1,537		868			—			(4	)		(3	)		(173	)		4			3,185
Operating Income		49		109		143			—			4			(1	)		(110	)		1			195
Other Income (Expenses)		14		9		(1	)		—			—			1	(d)		(2	)		(1	) (f)		20
Interest Charges		37		77		27			(3	)		—			—			(8	)		—			130
Income Before Income Taxes		26		41		115			3			4			—			(104	)		—			85
Income Taxes		9		15		39			1			2	(c)		—			(39	)		—			27
Income from Continuing Operations		17		26		76			2			2			—			(65	)		—			58
Preferred Stock Dividends		3		2		2			(2	)		—			—			—			—			5
Income from Continuing Operations Available to Common Stockholder	$	14	$	24	$	74		$	4		$	2		$	—		$	(65	)	$	—		$	53

The accompanying notes are an integral part of these unaudited pro forma condensed combined financial statements.

AMEREN ILLINOIS COMPANY

UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF INCOME

FOR THE SIX MONTHS ENDED JUNE 30, 2010

(In millions)

								Pro Forma
								Capital Structure Adjustments (a)			Push Down of Effects of Purchase Accounting			Elimination  of Intercompany Transactions			Distribution of AERG (e)			Ameren Illinois Company, Post-Distribution
	Historical
	CIPS		IP			CILCO
Operating Revenues:
Electric	$	321	$	501		$	319	$	—		$	—		$	(2	) (d)	$	(176	)	$	963
Gas		123		278			148		—			—			(1	) (d)		—			548
Other		1		4			40		—			—			(44	) (d)		—			1
Total operating revenues		445		783			507		—			—			(47	)		(176	)		1,512
Operating Expenses:
Fuel and purchased power		174		244			155		—			—			—			(77	)		496
Gas purchased for resale		79		176			104		—			—			—			—			359
Other operations and maintenance		87		146			126		—			(3	) (b)		(47	) (d)		(35	)		274
Depreciation and amortization		34		57			36		—			—			—			(20	)		107
Taxes other than income taxes		19		34			15		—			—			—			(2	)		66
Total operating expenses		393		657			436		—			(3	)		(47	)		(134	)		1,302
Operating Income		52		126			71		—			3			—			(42	)		210
Other Income (Expenses)		1		(1	)		1		—			—			—			(1	)		—
Interest Charges		14		45			23		(2	)		—			—			(10	)		70
Income Before Income Taxes		39		80			49		2			3			—			(33	)		140
Income Taxes		16		32			18		1			1	(c)		—			(12	)		56
Income from Continuing Operations		23		48			31		1			2			—			(21	)		84
Preferred Stock Dividends		1		1			—		(1	)		—			—			—			1
Income from Continuing Operations Available to Common Stockholder	$	22	$	47		$	31	$	2		$	2		$	—		$	(21	)	$	83

The accompanying notes are an integral part of these unaudited pro forma condensed combined financial statements.

AMEREN ILLINOIS COMPANY

UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF INCOME

FOR THE SIX MONTHS ENDED JUNE 30, 2009

(In millions)

								Pro Forma
								Capital Structure Adjustments (a)			Push Down of Effects of Purchase Accounting			Elimination  of Intercompany Transactions			Distribution of AERG (e)			Other Adjustments			Ameren Illinois Company, Post-Distribution
	Historical
	CIPS		IP		CILCO
Operating Revenues:
Electric	$	328	$	499	$	348		$	—		$	—		$	(2	) (d)	$	(196	)	$	1	(f)	$	978
Gas		131		290		157			—			—			—			—			—			578
Other		2		8		38			—			—			(44	) (d)		—			—			4
Total operating revenues		461		797		543			—			—			(46	)		(196	)		1			1,560
Operating Expenses:
Fuel and purchased power		200		275		133			—			—			—			(46	)		—			562
Gas purchased for resale		89		191		115			—			—			—			—			—			395
Other operations and maintenance		98		144		129			—			(2	) (b)		(46	) (d)		(36	)		1	(f)		288
Depreciation and amortization		34		57		34			—			—			—			(18	)		—			107
Taxes other than income taxes		18		34		14			—			—			—			(2	)		—			64
Total operating expenses		439		701		425			—			(2	)		(46	)		(102	)		1			1,416
Operating Income		22		96		118			—			2			—			(94	)		—			144
Other Income (Expenses)		4		1		(3	)		—			—			—			—			—			2
Interest Charges		14		52		15			(2	)		—			—			(3	)		—			76
Income Before Income Taxes		12		45		100			2			2			—			(91	)		—			70
Income Taxes		4		18		36			1			1	(c)		—			(35	)		—			25
Income from Continuing Operations		8		27		64			1			1			—			(56	)		—			45
Preferred Stock Dividends		1		1		—			(1	)		—			—			—			—			1
Income from Continuing Operations Available to Common Stockholder	$	7	$	26	$	64		$	2		$	1		$	—		$	(56	)	$	—		$	44

The accompanying notes are an integral part of these unaudited pro forma condensed combined financial statements.

AMEREN ILLINOIS COMPANY

Notes to Unaudited Pro Forma Condensed Combined Financial Statements

Note 1—Basis of Presentation

On October 1, 2010, CILCO and IP were merged with and into CIPS as part of a corporate reorganization of Ameren. Upon consummation of the Merger, CIPS’ name was changed to Ameren Illinois. Immediately following the Merger, Ameren Illinois distributed all of its shares of AERG common stock to Ameren with the subsequent contribution by Ameren of AERG stock to Ameren Energy Resources Company.

CIPS, CILCO and IP, all wholly owned (as to common stock) subsidiaries of Ameren, were entities under common control. Authoritative accounting guidance requires that transactions between entities under common control be valued and recorded at the historical cost basis of the parent. Accordingly, the financial statements of the receiving entity, CIPS, will reflect the transferred assets and liabilities of CILCO and IP at the historical cost basis of the common parent, Ameren.

Ameren’s historical cost basis in CILCO included purchase accounting-related adjustments in connection with Ameren’s acquisition of all of the outstanding common stock of CILCORP Inc. (“CILCORP”) in 2003. Such purchase accounting-related adjustments were components of Ameren’s basis in CILCO. As such, purchase accounting adjustments relating to CILCO’s rate-regulated electric and gas transmission and distribution businesses, recorded at Ameren, were pushed down to the financial statements of Ameren Illinois.

The AERG distribution was accounted for as a spin-off. Ameren Illinois transferred AERG to Ameren by distributing shares of AERG common stock to Ameren based on AERG’s carrying value. Subsequent to the AERG distribution, all AERG-related activity will be presented as discontinued operations in the Ameren Illinois financial statements.

Note 2—Pro Forma Adjustments

Balance Sheet

The following adjustments in the unaudited pro forma condensed combined balance sheet reflect the impact of events that are directly attributable to the Merger and the subsequent AERG distribution, assuming the Merger and the AERG distribution occurred on June 30, 2010:

(a) Reflects the impact of the redemption of all of CILCO’s outstanding preferred stock, the contribution of Ameren-owned IP preferred stock without consideration, and CIPS’ redemption of its 7.61% first mortgage bonds prior to the Merger. Also, includes the payout estimate and other costs related to CIPS and IP preferred shareholders who exercised their dissenters’ rights.

(b) Capitalized credit relating to retirement benefit costs for CILCORP’s rate-regulated utility businesses incurred from 2004 through 2006.

(c) Goodwill originating from Ameren’s acquisition of CILCORP’s rate-regulated utility businesses in 2003.

(d) Deferred income tax balances relating to purchase accounting adjustments originating from Ameren’s acquisition of CILCORP’s rate-regulated utility businesses in 2003.

(e) Accumulated other comprehensive income adjustment, net of income tax, relating to retirement benefits originating from Ameren’s acquisition of CILCORP’s rate-regulated utility businesses in 2003.

(f) Reflects the elimination of accounts receivable and accounts payable between CIPS, CILCO and IP.

(g) This column reflects the removal of AERG’s net assets as a result of the AERG distribution that occurred immediately after the Merger.

Statements of Income

The following adjustments in the unaudited pro forma condensed combined statements of income for each of the years ended December 31, 2009, 2008, and 2007, and for the interim periods of the six months ended June 30, 2010, and 2009, reflect the impact of events that are directly attributable to the Merger and the AERG distribution assuming both occurred on January 1, 2007:

(a) Reflects the impact of the redemption of all of CILCO’s outstanding preferred stock, the contribution of Ameren-owned IP preferred stock without consideration, and CIPS’ redemption of its 7.61% first mortgage bonds prior to the Merger.

(b) Retirement benefit expense credit that originated from Ameren’s acquisition of CILCORP’s rate-regulated utility businesses in 2003.

(c) The income tax impact of the retirement benefit expense credit.

(d) Reflects the elimination of transactions between CIPS, CILCO and IP related to electricity, natural gas, shared services and other agreements.

(e) This column reflects the removal of AERG’s results of operations as a result of the AERG distribution that occurred immediately after the Merger.

(f) Reflects the reversal of the elimination of transactions between AERG and Ameren Illinois after the AERG distribution was complete. These eliminations were necessary when AERG was a subsidiary of Ameren Illinois but are not necessary after the AERG distribution.