CONSOLIDATED BALANCE SHEETS (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current Assets
Cash and cash equivalents	$ 0	$ 0
Accounts receivable, net	397.4	269.9
Fair value of derivative contracts	273.7	257.3
Gas, oil and NGL	16.2	16.4
Materials and supplies	87.6	65.4
Prepaid expenses and other	43.7	45.2
Total Current Assets	818.6	654.2
Property, Plant and Equipment (successful efforts method for gas and oil properties)
Proved properties	8,172.4	6,874.3
Unproved properties, not being depleted	326.8	322.0
Midstream field services	1,463.6	1,360.5
Marketing and other	49.8	44.5
Total Property, Plant and Equipment	10,012.6	8,601.3
Less Accumulated Depreciation, Depletion and Amortization
Exploration and production	3,339.2	2,454.4
Midstream field services	297.5	244.6
Marketing and other	14.6	12.3
Total Accumulated Depreciation, Depletion and Amortization	3,651.3	2,711.3
Net Property, Plant and Equipment	6,361.3	5,890.0
Investment in unconsolidated affiliates	42.2	44.5
Other Assets
Goodwill	59.5	59.6
Fair value of derivative contracts	123.5	120.8
Other noncurrent assets	37.6	16.2
Total Other Assets	220.6	196.6
TOTAL ASSETS	7,442.7	6,785.3
Current Liabilities
Checks outstanding in excess of cash balances	29.4	19.5
Accounts payable and accrued expenses	457.3	332.2
Production and property taxes	40.0	18.9
Interest payable	24.4	28.1
Fair value of derivative contracts	1.3	139.3
Deferred income taxes	85.4	27.8
Current portion of long-term debt	0	58.5
Total Current Liabilities	637.8	624.3
Long-term debt, less current portion	1,679.4	1,472.3
Deferred income taxes	1,484.7	1,377.7
Asset retirement obligations	163.9	148.3
Fair value of derivative contracts	0	0.3
Other long-term liabilities	124.8	99.3
Commitments and contingencies
EQUITY
Common stock - par value $0.01 per share; 500.0 million shares authorized; 177.2 million and 175.9 million shares issued at December 31, 2011 and 2010, respectively	1.8	1.8
Treasury stock - 0.4 million and 0.1 million shares at December 31, 2011 and 2010, respectively	(13.1)	(3.8)
Additional paid-in capital	431.4	398.0
Retained earnings	2,673.5	2,420.0
Accumulated other comprehensive income	207.9	194.3
Total Common Shareholders' Equity	3,301.5	3,010.3
Noncontrolling interest	50.6	52.8
Total Equity	3,352.1	3,063.1
TOTAL LIABILITIES AND EQUITY	$ 7,442.7	$ 6,785.3