It may sound like a truism, but the world is actually running on petroleum. Everything is dependent on oil, from your car to the products in your local grocery store. Because, guess what: transportation, energy production and agriculture (read food) are heavily relying on petroleum and these are the back bones of our society.
Most of the people basically eat oil, because along with using it in powering tractors and stuff like that, the majority of fertilizers are made of petroleum.
Hence, in case of disaster, gas shortages are very probable and it would be a good idea to be prepared for such eventuality. In a survival situation, knowing how to store flammable items, like diesel, gas, propane or even wood could make the difference between life and death.