LIFO (Last-In First-Out, sometimes called FISH for First-In Still Here) is the successor of the Base Stock method of inventory accounting, the latter being declared illegal many years ago, because it does not fairly report income.
For income tax purposes LIFO remains legal & is the source of billions of dollars of somewhat "phantom" write offs, quite common practice in accounting for oil companies.
In short, it's a multi-multi blllion dollar boon to the such companies, reporting costs which bear little or no resemblance to economic reality.