Serbia’s oil system came under immediate strain Thursday after Washington let a sanctions waiver for Naftna Industrija Srbije (NIS) lapse, exposing the Gazprom Neft-linked refiner to U.S. measures and putting crude flows via Croatia’s JANAF pipeline on a short OFAC license that runs to October 15. Reuters reported that the move followed weeks of extensions, confirming the waiver’s expiry and its immediate operational impact. NIS operates the Pan?evo refinery and supplies about 80% of Serbia’s gasoline and diesel and over…