Customs duty exemption on specified oils and fats limits payable duty to notified reduced ad valorem rates on import. The Central Government exempts goods under specified headings and sub headings of the First Schedule to the Customs Tariff Act from so much of the duty leviable as is in excess of the amount calculated at the reduced ad valorem rates set out in the annexed Table, pursuant to sub section (1) of section 25 of the Customs Act, 1962.