Customs exemption for mineral oils from offshore zones bars proceedings and precludes duty refunds on earlier imports. The amendment deems mineral oils (including petroleum and natural gas) extracted or produced in the continental shelf or exclusive economic zone and imported before a specified historical cutoff to have been exempted from the whole of customs duties, bars any suit or proceeding in respect of such mineral oils, and provides that no refund of duties paid in respect of those mineral oils shall be made.