The Bureau of Mines has evaluated the extent of phosphate resources available for recovery by the experimental borehole mining method in the southeastern coastal plain of the United States. Phosphate resources at overburden depths greater than 30 m are, as a rule, currently unsuitable for recovery through conventional mining methods because of economic, environmental, or technical considerations. In the identified deposit areas, borehole mining operations are projected to yield a more favorable rate of return and to be environmentally more desirable than conventional surface mining. Borehole mining resource estimates presented in this study are preliminary and designed to serve as a basis for future resource evaluations, as the current data base is relatively sparse and incomplete. The resulting resources have, therefore, been classified as hypotheticl and speculative and are subject to updating as additional exploratory data become available. Hypothetical and speculative resources amenable to borehole mining are estimated to total about 385 billion metric tons (mt) of phosphate matrix with a minimum in situ grade of 5 pct p2o5. With projected borehole mining capabilities and current conventional beneficiation procedures, this resource would make available approximately 64 billion mt of phosphate rock product at an estimated grade of 30 pct p2o5.