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MOORPARK, CA - SEPTEMBER 23:  Smoke blows past oil wells at sunset on the eastern flank of the 16,000-plus-acre Guiberson fire, burning out of control for a second day as Red Flag warnings continue in southern California on September 23, 2009 near Moorpark, California. A Red Flag warning means critical wildfire weather, based on a combination of high temperatures, low humidity and Santa Ana winds, is occurring. Several large wildfires broke out in triple-digit temperatures on the first of Red Flag warnings.   (Photo by David McNew/Getty Images)
MOORPARK, CA - SEPTEMBER 23:  Smoke blows past oil wells at sunset on the eastern flank of the 16,000-plus-acre Guiberson fire, burning out of control for a second day as Red Flag warnings continue in southern California on September 23, 2009 near Moorpark, California. A Red Flag warning means critical wildfire weather, based on a combination of high temperatures, low humidity and Santa Ana winds, is occurring. Several large wildfires broke out in triple-digit temperatures on the first of Red Flag warnings.   (Photo by David McNew/Getty Images)

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This is the story of how one of the world's most important sources of energy lost half of its value in just six months. CNN's Rachel Crane reports.

The story behind the plunge in oil prices

This is the story of how one of the world's most important sources of energy lost half of its value in just six months. CNN's Rachel Crane reports.