Standard Oil is usually told as one story: John D. Rockefeller founded it in 1870, it grew to control roughly 90 percent of American oil production by 1900, and the United States Supreme Court ordered it broken into 39 independent companies in 1911 for violating the Sherman Antitrust Act. Read that way, 1911 is where the story ends. Standard Oil's own cited facts, followed a little further, tell a different story: the breakup was not an ending at all. It was the point where the modern American oil industry's map actually starts.
Look first at how Standard Oil got to 90 percent, because it used two different playbooks, not one. Its early growth came through horizontal integration, buying out competing refineries one by one until rivals simply stopped existing as separate companies. Its later growth came through a different strategy entirely, vertical integration, reaching down into the pipelines and distribution networks that moved oil to market rather than just the refineries that processed it; by 1890 that vertical reach alone gave Standard Oil control of 88 percent of the country's refined oil flows. A single company ran both strategies in sequence, first eliminating competitors, then controlling the infrastructure competitors would have needed to reach customers even if they had survived.
The 1911 ruling that ended that arrangement has a formal name most retellings drop: Standard Oil Co. of New Jersey v. United States. The Court did not simply fine the company or force it to change practices. It split Standard Oil into 39 independent companies, and the ruling's own record names the two largest of those pieces directly: Standard Oil's New Jersey subsidiary and Standard Oil of New York, which became known as Socony. Told as an ending, that is the last fact in the story. Followed one step further, it is a beginning: those two pieces are the direct ancestors of Exxon and Mobil.
Exxon and Mobil operated as separate companies for 88 years after the breakup that created them. In 1999 they merged again, forming ExxonMobil, one of the largest corporations in the world. An antitrust ruling meant to prevent one company from dominating the American oil industry ended up creating two of its own descendants that, given enough time, chose to become one very large company again. Standard Oil did not disappear in 1911. It multiplied, and decades later, two of the pieces it multiplied into found their way back to each other.