The following tables reflect information about our operating income (loss) by reportable segment (in millions): Refining Renewable Diesel Ethanol Corporate and Eliminations Total Three months ended March 31, 2020 Revenues: Revenues from external customers $ 20,985 $ 306 $ 811 $  $ 22,102 Intersegment revenues 2 53 64 (119 )  Total revenues 20,987 359 875 (119 ) 22,102 Cost of sales: Cost of materials and other 19,127 130 813 (118 ) 19,952 LCM inventory valuation adjustment 2,414  128  2,542 Operating expenses (excluding depreciation and amortization expense reflected below) 995 20 109  1,124 Depreciation and amortization expense 536 11 22  569 Total cost of sales 23,072 161 1,072 (118 ) 24,187 Other operating expenses 2    2 General and administrative expenses (excluding depreciation and amortization expense reflected below)    177 177 Depreciation and amortization expense    13 13 Operating income (loss) by segment $ (2,087 ) $ 198 $ (197 ) $ (191 ) $ (2,277 ) Refining Renewable Diesel Ethanol Corporate and Eliminations Total Three months ended March 31, 2019 Revenues: Revenues from external customers $ 23,218 $ 252 $ 793 $  $ 24,263 Intersegment revenues 2 51 52 (105 )  Total revenues 23,220 303 845 (105 ) 24,263 Cost of sales: Cost of materials and other 21,165 224 694 (105 ) 21,978 Operating expenses (excluding depreciation and amortization expense reflected below) 1,071 19 125  1,215 Depreciation and amortization expense 503 11 23  537 Total cost of sales 22,739 254 842 (105 ) 23,730 Other operating expenses 2    2 General and administrative expenses (excluding depreciation and amortization expense reflected below)    209 209 Depreciation and amortization expense    14 14 Operating income by segment $ 479 $ 49 $ 3 $ (223 ) $ 308 The following table provides a disaggregation of revenues from external customers for our principal products by reportable segment (in millions). Three Months Ended March 31, 2020 2019 Refining: Gasolines and blendstocks $ 8,244 $ 9,374 Distillates 10,663 11,917 Other product revenues 2,078 1,927 Total refining revenues 20,985 23,218 Renewable diesel: Renewable diesel 306 252 Ethanol: Ethanol 629 620 Distillers grains 182 173 Total ethanol revenues 811 793 Revenues $ 22,102 $ 24,263 Total assets by reportable segment were as follows (in millions): March 31, 2020 December 31, 2019 Refining $ 41,465 $ 47,067 Renewable diesel 1,632 1,412 Ethanol 1,614 1,615 Corporate and eliminations 3,036 3,770 Total assets $ 47,747 $ 53,864