Important Reminders Marginal production of oil and gas. The suspension of the taxable income limit on percentage depletion from the marginal production of oil and natural gas has been extended to tax years beginning after 1999 and before 2002. For more information on marginal production, see section 613A(c) of the Internal Revenue Code. Alternative minimum tax. Individuals, corporations, estates, and trusts who claim depletion deductions may be liable for alternative minimum tax. For more information on alternative minimum tax, see the following sources. If you are: See: An individual The instructions for Form 6251, Alternative Minimum Tax--Individuals. A corporation Form 4626, Alternative Minimum Tax--Corporations. An estate or trust Form 1041, U.S. Income Tax Return for Estates and Trusts, and its instructions.