HONG KONG—While oil’s rise above $50 a barrel for the first time in seven months is a landmark for the market, analysts appear to have no clear idea how long this year’s crude rally might last.

Brent crude, used to price much of the world’s oil, and West Texas Intermediate, the U.S. benchmark, both topped $50 a barrel Thursday before edging lower to $49.59 and $49.48 a barrel, respectively.

The...