The USGS model based on crustal abundance data and the reserve-abundance relationship of McKelvey, is applied to several metals in the Earth's crust (worldwide) and in the U.S. crust. The potential currently recoverable (present technology, economy) resources that come closest to the McKelvey relationship are those that have been sought for the longest time, such as copper, zinc, lead, silver, gold and molybdenum. Metals that do not follow the McKelvey relationship are ones that are byproducts (of major metals) or haven't been vital to the economy until recently (titanium, aluminum to a lesser degree).