U.S. natural gas prices have surged this week, breaking out of a narrow trading range with the largest single-day increase in more than 18 months and pushing up other benchmarks across the world.

A day after Henry Hub jumped 30 cents to finish at $2.10, the September contract gained another 9.2 cents to finish at $2.19 on Tuesday, surging past the long-term high established earlier this year. The prompt month held strong at $2.19 on Wednesday. Asian and European gas benchmarks have moved higher as well. While they declined slightly Wednesday, front-month contracts in Europe reached highs this week last seen in March.

“Henry Hub has been acting as a price floor on liquefied natural gas (LNG) markets, providing the marginal source of supply for Europe,” said Schneider...