Final answer:
In 2006, Exxon Mobil overtook Wal-Mart as the number one company on the Fortune 500 list, primarily due to high oil prices increasing its revenue and profits.
Step-by-step explanation:
The company that bumped Wal-Mart from the number 1 spot on the Fortune 500 list of largest companies in 2006 was Exxon Mobil. This significant achievement was primarily due to the soaring prices of oil at that time, which dramatically increased the revenue and profits of oil companies. Exxon Mobil's rise to the top of the Fortune 500 list illustrates the volatile nature of rankings as they can be influenced by shifts in market conditions and the performance of specific industry sectors.