Saudi Arabia probably has about 20% of the (currently economically) recoverable reserves. They do not really care if the price drops a lot more (it costs around $22 per barrel to extract, and they are already VERY wealthy). What they DO care about is that their economic "clout" and political influence will weaken if other sources of energy mean that they lose importance in the world economy. By allowing the price to fall they make North Sea oil extraction, shale gas and oil, and the Russian reserves uneconomic, thus preserving their own importance. These things have a way of "self correcting". If an economic boom follows a drop in energy prices, then demand will go up and so will the price.
