The allowance encouraged people who were taxed at a high marginal rate to invest in, perhaps risky, oil ventures.
Conversely if the venture was successful, an amount up to initial investment (under cost depletion, see below) would be tax free.
[4] (A) sulphur and uranium; and (B) if from deposits in the United States—anorthosite, clay, laterite, and nephelite syenite (to the extent that alumina and aluminum compounds are extracted from it), asbestos, bauxite, celestite, chromite, corundum, fluorspar, graphite, ilmenite, kyanite, mica, olivine, quartz crystals (radio grade), rutile, block steatite talc, and zircon, and ores of the following metals: antimony, beryllium, bismuth, cadmium, cobalt, columbium, lead, lithium, manganese, mercury, molybdenum, nickel, platinum and platinum group metals, tantalum, thorium, tin, titanium, tungsten, vanadium, and zinc.
(A) gravel, peat, pumice, sand, scoria, shale (except shale described in paragraph (2)(B) or (5)), and stone (except stone described in paragraph (7)); (B) clay used, or sold for use, in the manufacture of drainage and roofing tile, flower pots, and kindred products; and (C) if from brine wells — bromine, calcium chloride, and magnesium chloride.
All other minerals, including, but not limited to, aplite, barite, borax, calcium carbonates, diatomaceous earth, dolomite, feldspar, Fuller's earth, garnet, gilsonite, granite, limestone, magnesite, magnesium carbonates, marble, mollusk shells (including clam shells and oyster shells), phosphate rock, potash, quartzite, slate, soapstone, stone (used or sold for use by the mine owner or operator as dimension stone or ornamental stone), thenardite, tripoli, trona, and (if paragraph (1)(B) does not apply) bauxite, flake graphite, fluorspar, lepidolite, mica, spodumene, and talc (including pyrophyllite), except that, unless sold on bid in direct competition with a bona fide bid to sell a mineral listed in paragraph (3), the percentage shall be 5 percent for any such other mineral (other than slate to which paragraph (5) applies) when used, or sold for use, by the mine owner or operator as rip rap, ballast, road material, rubble, concrete aggregates, or for similar purposes.
U.S. Secretary of the Treasury Henry Morgenthau in 1937 declared the depletion allowance “perhaps the most glaring loophole” in the tax code.
United States President Franklin D. Roosevelt decried it and other tax-evasion stratagems by business “so widespread and so amazing, both in their boldness and their ingenuity, that further action without delay seems imperative.” The U.S. Congress refused to abolish the allowance corporate subsidy.