His massive operation netted him millions and millions of dollars. And in the twentieth century, he moved into investments across a broad base that left him one of the wealthiest men in the world. The family remains extremely wealthy today because of large holdings in Standard Oil and in a more-than-adequate portfolio that includes investments in many large financial institutions and corporations - just like many of the wealthiest people in America. Their money makes money because the have so much of it. They tend their crop of stocks, bonds and other holdings and continue to have all the financial resources they might possibly need or want.
John D. Rockefeller, it should be noted, gave away a great deal of money in the form of philanthropic support for education, health issues and other "needed" causes. He had always done so, even from his early beginnings. He gave half a billion dollars away over the years. And that was "back when" and the dollar bought a whole lot more. As just one example, he endowed a small Baptist college and, before the turn of the century, transformed it into a world-class educational institution. Guess where the first controlled fission reaction took place? Yup. University of Chicago campus.
The Rockefellers are probably best "classified" as being among the "super rich" today, and they have some of the deepest pockets around owing to large and diverse holdings. A link is provided below.