Observations of ozone (O3) and O3 precursors taken from aircraft flights over Houston, TX, Nashville, TN; New York, NY; Phoenix, AZ, and Philadelphia, PA show that high concentrations of reactive volatile organic compounds (VOCs) in the Houston atmosphere lead to calculated O3 production rates that are 2 to 5 times higher than in the other 4 cities even though NOx concentrations are comparable. Within the Houston metropolitan area, concentrations of VOCs and O3 production rates are highest in the Ship Channel region; the location of one of the largest petrochemical complexes in the world. As a consequence the concentration of O3 in the Houston metropolitan area has recently exceeded 250 ppb, the highest value observed in the U.S within the past 5 years.