Oil prices ticked up in early trading on Wednesday after ending the previous session up more than 4% on worries that the Iran-Israel conflict could disrupt supplies.

U.S. and global benchmark oil prices have seen their share of big moves since Israel launched attacks on Iran late last week, but there’s one indicator that helps investors put into perspective just how serious the situation is — and can become.

Oil prices resumed their upward climb and U.S. futures were lower early Tuesday after Israel’s military issued an evacuation warning to 330,000 people in Iran’s capital Tehran. Asian shares were mixed.