This is a bit of a trick question, because right now the most urgent requirement in the world is to find alternative energy resources, as we are running out of oil. But in physical terms, the world will never 'run out' of oil simply because we have not the technology nor the ability to remove every last drop from the reservoirs.
In most oil reservoirs, the oil is contained between the spaces of the sand grains (in a sandstone reservoir) or in the fissures and fractures in limestone reservoirs. Imagine a face sponge. It is made up of a series of tiny channels and pore spaces that allow the sponge to hold much more than its own weight of water. An oil reservoir is similar - when you get down to the microscopic level - a hard matrix of sand grains with lots of pore spaces and flow channels. If these channels get too narrow, and the sandstone is what is called 'oil wet', the attraction between the sandstone or limestone and the oil droplets becomes so strong that nothing will displace the oil - it hangs onto the rock like it was magnetised.
In a way, it is. Remembering that water and oil don't mix, if you place a drop of water onto an oily pan, what happens? The droplet rolls up into a ball because of the surface attraction of the water molecules. Similarly with an oil droplet. Place it on a water wet surface and they repel each other. So, even if the rock is 'water wet' and the oil rolls up into a ball, the surface attraction is so strong that you cannot apply enough pressure on the oil droplet to squeeze it through the spaces between the sand grains or the cracks in the limestone.
Even today, we are unable to extract more than about 55 to 60% of the oil in place. Before the latest technology was developed it was common practice to leave behind as much as 60% or more of the oil! But Man's ingenuity knows no bounds and many different methods have been tried to squeeze that extra drop of oil out of the formation, such as pumping hydrochloric acid down into a limestone reservoir, or hydrofluoric acid into a sandstone reservoir. This not only opens the pore spaces, but also 'water wets' the rock if it is 'oil wet', thereby changing the physical character of the rock.
Other processes, such as gas injection (to increase reservoir pressure) or even setting fire to the reservoir to thin the oil so it can be pumped more easily, have been tried. Even so, we still leave behind a good percentage of the original oil in place, upwards of 30 to 35%. In terms of already produced oil, that still runs into the billions of barrels of oil left in the ground.
So when someone tells you, 'We have plenty of oil', he's telling the truth. What he fails to tell you is that we are rapidly running out of 'useable oil', oil that people are willing to pay for. To extract any more will become horrendously expensive. And who's going to pay $300 for a tankful of gasoline?