Fuel efficient cars.
This was based on the idea that fuel prices will either remain stable or fall in this time scale. Just to remind people, China, India and other countries in the third world are enjoying economic growth which is leading to substantial increase in private car ownership. The effect is to increase world demand for Oil by about 1-2 million barrels of Oil per day per year. This article shows that even Saudi Arabia will max out the rate at which it can supply Oil at an extra 4 Million Barrels of Oil per day and that it will take them until well into the 2010's before the increased production is ready.
With an extra 2 billion people competing for the world's remaining Oil reserves, the only way gasoline will become cheap is if it surplanted as the transportation fuel of choice.