1981—Pub. L. 97–78 substituted “gilsonite (including all vein-type solid hydrocarbons),” for “native asphalt, solid and semisolid bitumen, and bituminous rock (including oil-impregnated rock or sands from which oil is recoverable only by special treatment after the deposit is mined or quarried)”.

1960—Pub. L. 86–705 included native asphalt, solid and semisolid bitumen, and bituminous rock.