Natural-gas prices swung higher on both sides of the Atlantic on Wednesday after Russia stopped exports to Poland and Bulgaria , a move that investors feared could portend deeper global supply strains ahead. Prices climbed as traders in Europe pondered whether Russia’s action against two of its neighbors in Eastern Europe foreshadows trouble in bigger markets such as Germany’s. In the U.S., trading was driven by the prospect that producers could continue to ship abroad as much natural gas as infrastructure allows in response to tighter supply abroad. Continue reading your article with a WSJ membership View Membership Options