In 2003 Range Resources, a natural gas company based in Fort Worth, Texas, was among the first of its competitors working on what appeared to be a promising deposit in Pennsylvania called the Marcellus Shale. Geologists had long believed the Marcellus was full of gas trapped in shale pores deep underground, like bubbles in fossilized soda. Range Resources was hoping to tap it with a method called hydraulic fracturing (or fracking for short) in which a high-volume mixture of water, sand, and chemicals is pumped into the shale under pressure. Several companies had used this approach to liberate natural gas from the Barnett Shale, a similar formation in Texas. When Range Resources fracked the Marcellus Shale, the yields were at first modest. So the company shifted its approach; instead of drilling vertical wells straight into the shale, they drilled wells that could also turn sideways thousands of feet below the surface and then probe horizontally for miles in any direction. With horizontal drilling, the yields got steadily better, until Range Resources hit a jackpot in 2006: a gas-rich formation that might generate 50 years of profits for the company, according to spokesman Matt Pitzarella. That discovery helped confirm that the Marcellus—which cuts across portions of at least eight eastern states from New York to Tennessee—is one of the largest shale gas deposits in the world. A $400 million company in 2003, Range Resources is now valued at more than $8 billion, largely because of its Marcellus lease holdings.1 Meanwhile, the combination of fracking and horizontal drilling has sent potentially recoverable amounts of natural gas nationwide soaring. The Energy Information Administration estimates that technically recoverable shale gas reserves have the potential to satisfy domestic consumption in the United States (based on 2010 figures2) for more than 30 years.3 But for shale gas to meet its potential, millions of Americans will have to live with drill rigs in or near their own neighborhoods. And that opens the door to a range of potential environmental health problems: pipelines and wellheads can explode, the process produces toxic air emissions, and fracking generates liquid wastes that can contaminate surface and drinking water supplies. The fact that many gas companies—citing confidential business practices—won’t readily disclose their fracking chemicals has also become a public relations issue for the industry. According to an April 2011 report for the U.S. House of Representatives Committee on Energy and Commerce, oil and gas service companies use 750 chemicals during fracking,4 some of them—for instance, salt, citric acid, and coffee—fairly innocuous as far as adverse human health effects are concerned, and some not. Naphthalene, xylene, toluene, ethylbenzene, and formaldehyde, for example, each used in a number of proprietary fracking solutions, are known or suspected human carcinogens.5 On 17 June 2011 Texas became the first state to require that drillers publicly disclose their fracking chemicals.6