We are so reliant on cars and modern transport we would be in a very difficult position if we suddenly found that we were unable to buy petrol or diesel, possibly through problems of suppliers, financial etc.
We would be unable to travel to work or go to the supermarket for our groceries, buses and trains would stop, this would be particularly difficult for people living in rural areas that are not within walking distance of shops. Assuming that there is a way of transporting goods, possibly back to the horse and cart and local farmers.