Inventories	6 Months Ended
Inventories	Jun. 30, 2020
Inventories [Abstract]
Inventories	Note 3—Inventories Inventories consisted of the following: Millions of Dollars June 30 December 31 2020 2019 Crude oil and natural gas $ 452 472 Materials and supplies 530 554 $ 982 1,026 Inventories valued on the LIFO basis totaled $ 352 million and $ 286 million at June 30, 2020 and December 31, 2019, respectively. Due to a precipitous decline in commodity prices beginning in March this year, we recorded a lower of cost or market adjustment in the first quarter of 2020 of $ 228 million to our crude oil and natural gas inventories. The adjustment was included in the “Purchased commodities” line on our consolidated income statement. Commodity prices have since improved in the second quarter.