Situating Edith Wharton in the context of America's accelerating petro-culture, this essay argues that her novels critique a society that takes for granted high-volume, nonrenewable energy, and specifically revolutionary new kinds of energy: petroleum, natural gas, and the fossil-fueled power stations necessary for the large-scale, continuous production of electricity. Attention to the idiom of energy in The House of Mirth and its mirror text, The Custom of the Country, along with Ida Tarbell's History of Standard Oil and Theodore Roosevelt's conservationism, sheds new light on assumptions about moral agency, personal freedom, changing modes of thought, and the environment between 1880 and World War I. The essay shows how Wharton's allegorical treatment of Lily Bart and Undine Spragg anticipates the notion of externalities or consequences of industrial activities that affect outside parties but are not reflected in the cost of production.