Inventories	9 Months Ended
Inventories	Sep. 30, 2020
Inventories [Abstract]
Inventories	Note 3—Inventories Inventories consisted of the following: Millions of Dollars September 30 December 31 2020 2019 Crude oil and natural gas $ 503 472 Materials and supplies 531 554 $ 1,034 1,026 Inventories valued on the LIFO basis totaled $ 373 million and $ 286 million at September 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 improved since the first quarter.