Table of Contents December 31, (Millions of dollars) 2020 2019 Deferred income tax assets: Tax carryforwards $ 1,346 $ 1,218  Postemployment benefits other than pensions 919 876  Pension 396 445  Warranty reserves 247 263  Research expenditures 193 219  Allowance for credit losses 126 171  Post sale discounts 153 200  Other employee compensation and benefits 186 197  Lease obligations 154 157  Stock-based compensation 81 107  Other—net 317 250  4,118 4,103  Deferred income tax liabilities: Capital and intangible assets, including lease basis differences (1,526) (1,574) Bond discount (117) (122) Translation (147) (194) Other outside basis differences (284) (257) Undistributed profits of non-U.S. subsidiaries (95) (118) (2,169) (2,265) Valuation allowance for deferred tax assets (1,009) (928) Deferred income taxes—net $ 940 $ 910  The components of deferred tax assets and liabilities were: At December 31, 2020, approximately $1,399 million of U.S. state tax net operating losses (NOLs) and $139 million of U.S. state tax credit carryforwards were available. The state NOLs primarily expire over the next twenty years. The state tax credit carryforwards primarily expire over the next fifteen years, with some credits having an unlimited carryforward period. In total, we have established a valuation allowance of $183 million related to certain of these carryforwards. At December 31, 2020, approximately $350 million of U.S. foreign tax credits were available to carryforward on the U.S. federal tax return. These credits have a ten-year carryforward period and begin to expire in 2028. At December 31, 2020, amounts and expiration dates of net operating loss and interest carryforwards in various non-U.S. taxing jurisdictions were: At December 31, 2020, non-U.S. entities that have not yet demonstrated consistent and/or sustainable profitability to support the realization of net deferred tax assets have recorded valuation allowances of $803 million, including certain entities in Luxembourg. A reconciliation of the beginning and ending amount of gross unrecognized tax benefits for uncertain tax positions, including positions impacting only the timing of tax benefits, follows. 94 (Millions of dollars) 2021 2022 2023 2024-2026 2027-2041 Unlimited Total $ 45  $ 81  $ 10  $ 79  $ 819  $ 3,929  $ 4,963 