It doesn't even matter overly much if that barrel is selling for $80 rather than $100. The rule of thumb is that every 10% rise in the price of oil cuts global economic growth by a third of a percentage point over the following year. So if oil is at $100 a barrel in 2008 rather than $80, the projected global GDP growth rate of 5.2% would be cut to 4.4%. A hit to growth, yes, but not a plunge into recession.
read the Forbes article