LONDON—Banks raised their forecasts for oil prices for the seventh month in a row in April on the back of heightened geopolitical risks and OPEC-led production cuts.

The price of Brent crude, the global benchmark, has risen roughly 50% over the past year, bolstered by the Organization of the Petroleum Exporting Countries’ deal to cut production and tensions in the Middle East that could threaten supply.

Brent...