Oil prices gained for a fourth straight day on Thursday, as investors worried about supply shortages amid U.S. President Donald Trump's push for a swift resolution to the war in Ukraine and threats of tariffs on countries buying Russian oil.

September Brent crude futures, which expire on July 31, slipped 10 cents, or 0.1%, to $73.14 a barrel. The more active October contract fell 14 cents, or 0.2%, to $72.33. U.S. West Texas Intermediate crude for September delivery dropped 5 cents,