Oil prices are again marching higher, prompting talk that crude could reach $100 a barrel for the first time since 2015’s crash.

Brent crude, the global benchmark for oil prices, jumped 4.1% in the third quarter to $82.72 a barrel, the highest level in nearly four years. Brent’s fifth consecutive quarterly advance marks its longest such streak since 2008. U.S. crude edged down from its most recent multiyear high, falling 1.2% to $73.25 a barrel last quarter, though it has risen in five of the past six weeks. Investors have...