According to the Energy Information Administration, world demand for oil in 2007 was over 31 billion barrels (.xls), and current proven reserves are calculated to be just over 1.3 trillion barrels (.xls). 1.3 trillion / 31 billion = nearly 43 years' worth of oil at 2007 levels of consumption.
In 1980 (.xls), the equation was:
645 billion / 23 million = 28 years' worth of oil at 1980 levels of consumption.
To use an analogy I have come across a few times, talking about the "proven reserves" of one's personal supply of food would consider only the contents of one's pantry, rather than what could be obtained at the grocery store once supplies had run low.
Someone careful might be able to convince me that the real problem is that there's too much, not too little, of the black gold.