On July 1, an estimated 42,000 gallons of crude oil poured out of ExxonMobil's Silvertip pipeline and into the Yellowstone River in Montana. Significant accumulations of oil have been found more than 40 miles downriver, and traces of oil have floated twice as far. While the cause of the spill has not been determined, speculation has centered on high river waters that could have exposed the pipe to damage.