Summarized Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2011

Summarized Quarterly Financial Data (Unaudited) [Abstract]

Summarized Quarterly Financial Data (Unaudited)

15. Summarized Quarterly Financial Data (Unaudited)

	Quarter Ended
(Thousands of Dollars)	March 31, 2011		June 30, 2011			Sept. 30, 2011			Dec. 31, 2011
Operating revenues	$	381,209		$	433,289		$	522,921		$	370,146
Operating income		29,499			53,433			92,885			24,780
Net income		10,238			24,672			48,581			6,410

	Quarter Ended
(Thousands of Dollars)	March 31, 2010		June 30, 2010			Sept. 30, 2010			Dec. 31, 2010
Operating revenues	$	381,482		$	398,449		$	467,424		$	365,635
Operating income		30,828			54,051			76,937			21,621
Net income		7,699			24,396			39,189			6,783

- Definition

The entire disclosure for the quarterly financial data in the annual financial statements. The disclosure may include a tabular presentation of financial information for each fiscal quarter for the current and previous year, including revenues, gross profit, income or loss before extraordinary items and earnings per share data. It also includes an indication if the information in the note is unaudited, comments on the aggregate effect of year-end adjustments, and an explanation of matters or transactions that affect comparability or are pertinent to an understanding of the information furnished.

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