The gap comes down to what each mogul actually owned versus controlled. Rockefeller's $340M figure is wildly understated—his actual inflation-adjusted wealth exceeded $11 billion, but the description uses a conservative snapshot. However, Harriman's advantage wasn't just size; it was structural. Railroads were the foundational infrastructure of industrial America, while oil was a commodity within that system. Harriman owned outright the physical assets (tracks, stations, equipment) that literally moved goods across the continent. His monopoly was geographic and regulatory—you couldn't build competing rail lines through the same mountain passes. Rockefeller's monopoly was operational; competitors could theoretically refine oil elsewhere, which is precisely why antitrust eventually shattered it.

The revenue streams tell the real story. Harriman's railroads extracted value from every transaction moving across America for decades—farmers, manufacturers, consumers all paid tolls to his network. It was a recurring, inescapable tax on commerce. Rockefeller's $90M annual revenue from oil refining was massive, but oil refining itself was high-velocity; you extract, refine, sell, repeat. Railways are different—the asset generates perpetual revenue just by existing. Once Harriman built those thousands of miles, they worked for him every single day without reinvention.

The antitrust angle also reveals why Harriman stayed richer longer. When Standard Oil got broken up in 1911, Rockefeller's empire fragmented into competing pieces—Standard Oil of New Jersey, Standard Oil of California, Socony, etc. His wealth got distributed across multiple companies with diluted control. Harriman died in 1909, just before the major railroad trust-busting began, so his family inherited an intact, still-monopolistic network. His heirs controlled the same irreplaceable infrastructure for generations. That's the difference between owning indispensable infrastructure versus owning a market position—one is permanent, the other is political.