Chevron earnings fall 33% San Francisco Chronicle Copyright 2012 San Francisco Chronicle. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Updated 8:38 p.m., Friday, November 2, 2012 Hit by declines in both oil production and prices, Chevron Corp. said Friday that its third-quarter net income fell 33 percent. The sluggish global economy has cut into worldwide demand for energy products, from gasoline and diesel to jet fuel. Concerns about economic growth have caused oil and natural gas prices to fall, hurting the bottom line for oil producers. Michael Wirth, who leads Chevron's global refining and marketing operations, said Friday that such price spikes could become more common if the state pushes ahead with regulations to fight global warming. California, which already uses its own pollution-fighting gasoline blends not found in other states, will soon require refineries to lower the greenhouse gas emissions associated with the fuel they produce. Chevron sold oil and natural gas liquids for $91 per barrel in the United States. during the quarter, compared with $97 per barrel a year ago.