Receivables

Our trade receivables are generally not collateralized. At December 31, 2014 and December 31, 2013, 39% and 34% 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.

While we are continuing to collect payment on some of our receivables from our primary customer in Venezuela, the amount of outstanding receivables has increased in connection with increased activity. These receivables are not disputed, and we have not historically had material write-offs relating to this customer. Our total outstanding trade receivables in Venezuela were $670 million, or approximately 9% of our gross trade receivables, as of December 31, 2014, compared to $486 million, or approximately 8% of our gross trade receivables, as of December 31, 2013. Of the $670 million of receivables in Venezuela as of December 31, 2014, $256 million has been classified as long-term and included within “Other assets” on our consolidated balance sheets. Of the $486 million receivables in Venezuela as of December 31, 2013, $183 million has been classified as long-term and included within “Other assets” on our consolidated balance sheets.

The following table presents a rollforward of our allowance for bad debts for 2012, 2013, and 2014.



Millions of dollars	Balance at Beginning of Period		Charged to Costs and Expenses			Write-Offs			Balance at End of Period
Year ended December 31, 2012	$	137	$	(40	)	$	(5	)	$	92
Year ended December 31, 2013	92		39			(14		)	117
Year ended December 31, 2014	117		26			(6		)	137