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The two historically dominant commercial processes are gaseous diffusion enrichment and gas centrifuge enrichment. The first exploits differences in molecular transport through a barrier; the second exploits mass-dependent redistribution in a rotating gas. Both are isotope-separation principles rather than chemical separation of uranium from another element.

gas centrifuge enrichment had become predominant by the time of this examination. Its much smaller electricity demand reduces a major operating cost of diffusion technology. Modular capacity and the replacement of ageing diffusion plants contributed to commercial adoption. This historical conclusion does not require machine dimensions, operating conditions or a cascade design. The United States' final operating diffusion plant closed in 2013, consistent with the earlier transition rather than a claim based on current plant counts.^[ref]