Receivables

12 Months Ended

Dec. 31, 2011

Receivables [Abstract]

Receivables

Note 3. Receivables

Our trade receivables are generally not collateralized. At December 31, 2011, 45% of our gross trade receivables were from customers in the United States. At December 31, 2010, 36% of our gross trade receivables were from customers in the United States. No other country or single customer accounted for more than 10% of our gross trade receivables at these dates.

The following table presents a rollforward of our allowance for bad debts for 2009, 2010, and 2011.

	Balance at		Charged to
Millions of dollars	Beginning of		Costs and				Balance at
Allowance for bad debts	Period		Expenses		Write-Offs		End of Period
Year ended December 31, 2009:	$	60	$	37	$	(7)	$	90
Year ended December 31, 2010:		90		5		(4)		91
Year ended December 31, 2011:		91		53		(7)		137