Oil has moved up the past two trading days, to a large extent because of a rebel attack on part of the Shell pipeline system in Nigeria. Bloomberg reports "the strike targeted two well clusters in the western Niger River delta." Such incidents are fairly frequent now.
The CIA World Factbook lists Nigeria as only the number 14 producer of oil in the world. If a problems there can push up the price of oil, how bad are the risks in regions that are even larger producers? Certainly a disruption in supply from a country that is a exporter than Nigeria could move crude up by a few dollars.