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Inventories (Tables)
12 Months Ended
Dec. 31, 2020
Inventory Disclosure [Abstract]  
Schedule of Inventory
Inventories consisted of the following at December 31, 2020 and 2019.
December 31,
(Thousands of dollars)
20202019
Unsold crude oil$16,399 27,634 
Materials and supplies49,677 48,489 
Inventories$66,076 76,123