Economics do matter. If you do not look economics, the oil in the Canadian tar sands is enough to provide the world with 50 years of oil at current consumption levels.
Over the last five years the global oil reserves have increased a lot because of the tar sands in Canada and Venezuela. With the falling price of oil the economics of new tar sands production becomes questionable and that reduces the oil reserves in both countries dramatically. It also reduces the oil reserves of Brazil and the US because in both cases much of the new oil that has come online in the last five years is more expensive to extract than the current price of oil.
|Notice the dramatic rise in the two tar sands countries oil reserves|
With a lower price of oil this reserves go away
If I were to estimate it, the fall in the price of oil has made around one quarter of the oil reserves no longer economic to extract and therefore no longer part of the oil reserves. This has taken the global oil reserves from a 40 year supply at current consumption levels to 30 years.
The price rise over the last decade were mainly because there was a narrow margin between oil produced and oil consumed. The high price brought a lot of new production online which now has lead to an excess of oil in the market place and a falling price.
Where will things go? Everything depends on the price of oil and the cost to extract it. If the prices falls further the oil reserves will fall further. The cost of extraction can fall due to improved technology. Extraction costs can also rise due to political instability. There is no real reason to expect prices to rise much in the next five to ten years especially if we are headed towards a global recession and there are indicators out there, like the dramatic fall in the Baltic Dry Index, that show this could be possible.