Today, the price of oil hit a record high of $43.05 a barrel (UPDATE). A combination of excessive demand, uncertainty, and a lack of spare producation capacity have combined to create this price. This situation, as it persists through this fall/winter, is a window of vulnerability that can be exploited by global guerrillas. A series of well orchestrated GG attacks on Saudi, Caspian, and Iraqi oil infrastructure (while these conditions persist) would drive the price over $100 and keep it there.
The economic effects of this exploitation would be decisive. A short term spike in oil prices (2-5 months that average over $75 a barrel) would plunge the world into recession, spike the US budget deficit, and put many nations in the developing world at the brink of state failure (a good outcome for GGs). The only real question is whether operational GGs have developed a strategic understanding of their current capacity to control global markets and national economies.
If they did, they would likely attack. The negative strategic repercussions for global guerrillas would be minimal. The short term nature of the spike would not necessarily benefit OPEC, since much of the benefit in improved prices would go to financial speculators (lost to the industry). Additionally, the volatile nature of the price increase wouldn't necessarily increase the level of investment in new production (particularly if prices were allowed to drop after this period of intense activity).