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Inventories (Tables)
6 Months Ended
Jun. 30, 2016
Inventory Disclosure [Abstract]  
Summary of Inventories
Inventories consisted of the following:

 
Millions of Dollars
 
June 30
2016

 
December 31
2015

 
 
 
 
Crude oil and petroleum products
$
3,725

 
3,214

Materials and supplies
268

 
263

 
$
3,993

 
3,477