A groundswell of interest in oil and gas production from shales is transforming the domestic industry. It's a surprising development for such an unassuming rock. After all, shales are the epitome of quiet-formed during eons of slow and steady deposition, undisturbed by great gushes of sediments from rivers or the busy, colorful lives of reef dwellers. Shales are the tortoises among the world's hydrocarbon reservoirs, often under-appreciated and, until recently, often overlooked. But the rousing success of the Barnett shale play in the Fort Worth Basin, and the emergence of the Fayetteville and Woodford as powerhouses in the Arkoma Basin, have inspired evaluation of shale plays throughout the country. The major lesson operators have learned in their fresh look at shales as reservoirs is that each play is unique. Many distinct characteristics work together in various combinations to yield commercial quantities of oil and gas. Target shales need certain geologic parameters, the correct drilling and completion technologies, and strong commodity prices to make economic sense. And commercial shale plays-for both oil and gas-appear to be present throughout the geologic section. Here's a tour, from oldest to youngest, of several rising shale plays and the operators that are pushing them into the mainstream. For more on this, see the July issue of Oil and Gas Investor. For a subscription, call 713-260-6441.