I decided to do a little math to find out how many electric vehicles need to hit the road to displace all the oil imported from OPEC countries. It turns out, about 42% or 105 million vehicles.
According to eia.gov, in 2012 we imported 1,557,591,000 barrels of oil from OPEC countries. According to a reuters article, 2012 passenger vehicles sold averaged 23.8 mpg. Though the actual average fuel economy for all vehicles on the road would include previous years and be less, I'll be conservative and use 24 mpg. Also, we'll use average miles driven per year to be 15,000.
Barrels of oil used by a vehcile in one year is:
15,000 miles / 24 miles/gallon / 42 gallons / barrel of oil = 14.9 barrels of oil
How many ICE vehicles need to be removed to replace all OPEC oil?
1,557,591,000 barrels / 14.9 barrels/car = 104670115 vehicles
So about 105 million ICE vehicles to be replaced by electric vehicles. A few searches show there about 250 million vehicles on the road so that's about 42%.
Why did I mention Tesla specifically? Because the Model S has sufficient range to be a primary vehicle. I don't think electric vehicles with range < 200 miles will appeal to enough people. Vehicles like the Nissan Leaf and the Chevy Volt certainly help reduce oil usage, but I think Tesla building the S, X, and E (3rd generation) will have the most impact.