Some companies that consume large quantities of oil keep their own oil reserves for years in which average oil prices are exceptionally high. Thus, at times when oil prices are quite high, they can partially deplete their reserves, using oil that they bought earlier at lower prices, with the intention of buying oil to add back to their reserves when average oil prices are lower. Nevertheless, last year, when average oil prices were astronomically high throughout the year for geopolitical reasons, not all of these companies partially depleted their reserves.
Which of the following, if true, best explains why not all of these companies partially depleted their reserves?