Time on the Cross: The Economics of American Negro Slavery (1974, written with Stanley Engerman)—in which was collected and analyzed massive data showing that slavery was a far more profitable economic institution than had been previously thought—Fogel had already generated controversy among historians with his earlier work, Railroads and American Economic Growth: Essays in Econometric History (1964), in which he argued that the U.S. economy in the 1800s would have grown at the same rate, even if railroads had not existed. He was a pioneer in the application of quantitative methods to economic history, dubbed "cliometrics," and in the development of the use of counterfactuals among historians.
More recently, Fogel had focused on, in his words, “the problem of creating and studying larger life-cycle and intergenerational data sets.” The result was many research papers, articles and books on the economics of aging. His most recent book is Political Arithmetic: Simon Kuznets and the Empirical Tradition in Economics (University of Chicago Press, 2013); Kuznets was Fogel's thesis adviser at Johns Hopkins.
Obituaries abound; examples can be found in the New York Times, The Economist, the Los Angeles Times, the Washington Post, and at the University of Chicago. Sir Roderick Floud has also posted a substantive commentary on the EHS website.