No Oil Producing and Exporting Cartels Act of 2018 or NOPEC This bill amends the Sherman Act to prohibit a foreign state from engaging in collective action impacting the market, supply, price or distribution of oil, natural gas, or other petroleum product in the U.S. Specifically, a foreign state is prohibited from: collective action that limits the production or distribution of such product, collective action to set or maintain the price of such product, or any other action that restrains trade of such product. Sovereign immunity (i.e., a foreign state's immunity from the jurisdiction of U.S. courts) and the act of state doctrine (i.e., the prohibition of a court invalidating an official act of a foreign sovereign performed within its own territory) shall not apply to a foreign state's violation of this bill.