The Dow Jones Industrial Average jumped 300 points at the open on Friday, buoyed by renewed hopes that the US and Iran might actually reach a peace agreement. The S&P 500 edged slightly higher, but the overall picture was decidedly mixed, with investors split on whether this latest round of diplomatic optimism is the real thing or just another false start.

Dow futures had earlier surged as much as 422 points, or 0.8%, before settling back.

The Iran factor and why oil matters here

The rally traces back to statements from President Trump suggesting progress on a deal with Iran. The potential reopening of the Strait of Hormuz, the narrow waterway through which a massive share of global oil shipments pass, is the centerpiece of investor optimism.

When peace signals emerge from the Middle East, oil prices tend to drop. That’s exactly what happened, with crude declining on the latest headlines. Oil prices have fallen by more than 4% on previous peace signals during this conflict.