There are a lot of news stories in the trades that the Saudis really cannot sustain a $40/bbl price, even though they say they can. They have a lot of projects they need to keep going in order to placate their somewhat restive population. But they also have a ton of cash. So they can let prices fall for a while, but long term, here's what energy economist Matthew Hulbert [who has been pretty good historically] published in the European Energy Review in 2012:
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Notice that their budgetary breakeven price is nearly two orders of magnitude greater than the $2/bbl profitability the media nincompoops keep talking about. Notice also, that everyone North of Saudi Arabia needs prices over $106/bbl. They're ALL toast.
People haven't talked much about firming prices on the demand side, but that is going to happen. Germany is shutting down their nuclear energy, and Japan may also scale back nuclear [in Japan's case, what's going to happen isn't clear. They're moving slowly on this, and by the time significant nuclear energy production scalebacks might occur, public sentiment in Japan may not be as antinuclear as it is now in the wake of Fukishima.] And US consumers have traditionally shown that they will go back to bigger cars, SUVs and trucks as gas prices fall.