Oil prices on Monday skidded to their biggest single-day declines in more than three months, as gyrations in Chinese stocks and the prospect of more crude from the U.S. and Iran revived worries about the global supply glut. Iran is nearing an historic nuclear deal with the West — and that’s scaring the oil markets. Oil prices plunged nearly 8% and broke below $53 a barrel on Monday, the deepest plunge for crude oil since early February. The U.S. benchmark oil price slid for the third trading session in a row, closing down $4.38, or 7.7%, to $52.53 a barrel on the New York Mercantile Exchange. Monday’s losses are the biggest in percentage terms for a single session since February, though they also included declines during limited electronic trading on the Friday holiday. Nymex crude settled at its lowest level since April 13.

Iran deal nears: The Iran factor is more influential on oil prices than Greece. Iran has 158 billion barrels of oil reserves, but that oil has been largely blocked from the global markets due to sanctions against Iran.