There was, of course, one exception: oil. Many of the chemistry-for-colonies exchanges the United States made, including synthetic rubber and plastic, involved substituting petroleum for other materials. In 1945, when 59 percent of the world’s proven oil reserves lay within U.S. borders, this gave the United States an extraordinary measure of self-sufficiency. But as those reserves got used and large ones opened in other countries, oil became increasingly foreign in provenance.
