Petroleum is one of the most profitable of Texas industries, but it is also the likeliest culprit for its smog. According to the Environmental News Service, a new study from the U.S. Department of Energy has identified specific volatile compounds (VOCs) in petroleum as the source of much of Houston's smog. The study's resolution is especially surprising, as petroleum had not previously been suspected as an element in smog. Samples taken from Houston's air showed levels of ozone concentration far exceeding the EPA's safety standards. But with this finding, more effective approaches to controlling air pollution can now be sought for one of America's most smog-afflicted cities.