Seems like a weird thing to ask. However, ExxonMobil posed this question in their blog because they want to make a point: petroleum will still be used by 90% of the world's transportation fleet by 2040, because it can pack an energy punch. They think that the world won't be able to create something that generates enough power to displace traditional oil products.
So, how much would it take? If you somehow got to adjust your iPhone to run on gasoline, you would be able to charge it once a day for almost 20 years! This is because oil products have a high energy density. As of now, very few other forms of producing energy have the effectiveness that oil products have.
This, of course, doesn't take into account the environmental, and political issues that the usage of oil causes around the world. Still, it illustrates how long the road ahead is until we can stop using dirty-burning fuels to power our society.