My teacher says that there are about 200 years of oil deposits left, but my text book says there are only about 30 years of oil left underground. Who is right?

Lydia's answer is quite correct, however, I side with your teacher. Over 25 years ago there was an oil 'shortage' caused not by the lack of oil, but by the refusal of the oil rich Arabian countries to produce it due to the Middle East conflicts. We all did panic, and the race was on to find alternative fuels or oils within our own non-Arab regions. Now here we are 25 years later, and there is more than enough oil for all, at prices adjusted for inflation that are far cheaper than they were in the 70's. Further, technology will find new fuel sources or new oil over the next 20 years. And Power plants have made coal and natural gas their 'fuel of choice', further reducing our dependence on oil. Teacher knows best.