1. Our oil supplies are limited because there is only a fixed amount of it in the world and it also takes time to discover and extract it.
2. It took millions of years of heat and pressure to make the oil we have today, it would take millions more to produce more oil.There are different theories about this.
3. According to peak oil theory we have already hit our high point in oil production and in future it will decline.Crud oil will last 50 years but there are no drilling potentials in many areas because of border conflicts.
4. Prediction for future oil supplies depend on many different factors, and there are many places on the globe where we have not explored yet. Technology is another factor affecting oil supplies. If we can learn how to exploit the tar sands, deep oil deposits in the ocean, and perhaps explore the polar region, we could extend our oil supply significantly. Differing assumptions about the amount of oil we could get to and the technology we develop to exploit it can make estimates vary widely.