Oil futures are getting pummeled Monday. Prices for West Texas Intermediate and Brent crude are poised for their lowest settlements in three months. In fact, crude prices have cratered nearly 12% since June 24.

Monday’s action marks the sharpest one-day drop since April, as August crude on the New York Mercantile Exchange traded at $53.28 a barrel, down $3.67, or more than 6.5%. On the ICE Futures exchange, August Brent crude lost $2.97, or 4.92%, to $57.38 a barrel.

Click ahead for the five biggest reasons for the dramatic price plunge:

Greek voters on Sunday rejected demands by the country’s creditors. That raised the risk of Greece’s potential exit from the eurozone, which the oil market believes could impact energy demand from Europe. “Even though Greece is a particularly small consumer of oil, it is the risk of contagion and in a worse case, another recession in the eurozone, which has weighed on oil prices,” said Thomas Pugh, commodities economist at Capital Economics. Read the latest news on Greece.

Tuesday marks the deadline for a final agreement between the West and Iran over Iran’s nuclear program. Iranian Foreign Minister Javad Zarif on Friday implied that the parties were closing in on a final pact. An Iranian nuclear deal “would lead to lifting of sanctions and enable the country to export oil once again,” said Colin Cieszynski, chief market strategist at CMC Markets. Analysts have said Iran has the ability to add millions of barrels of oil to the global market and usher a quick return to $50 Nymex oil prices or lower. A top oil adviser, however, has said that Iran may delay the launch of new oil contracts by three months until December to take advantage of a potential lifting of western sanctions.

Last week, the Energy Information Administration reported the first weekly increase in U.S. crude supplies since April and Baker Hughes weekly data showed that the number of U.S. rigs actively drilling for oil rose for the first time this year. “There has been mounting evidence that U.S. oil production is set to pick up again,’ said Capital Economics’s Pugh. “The partial recovery in the oil price over the last few months is consistent with a pick up in the total active rig count, and this is finally starting to show through in the hard data.

Signs of slower growth in China have raised concerns that demand in the world’s second-largest importer of oil may be weakening,” said Capital Economics’s Pugh. He pointed out that Chinese oil imports fell by 10% year on year in May. A “dramatic drop” in Chinese equities Monday, with the Hang Seng Composite index down 3.8%, “also suggests potentially weaker demand for oil moving forward,” said Tim Evans, chief market strategist at Long Leaf Trading Group. Still, Pugh said he doesn’t expect oil demand growth in China to fall much further. “There are signs that the opportunistic buying, which occurred when oil prices first dropped, has run its course,” he noted.

Oil production in May from the Organization of the Petroleum Exporting Countries climbed to its highest monthly level since October 2012, according to a Platts survey of OPEC and oil industry officials and analysts released in mid-June. Reports due out in the coming days may provide further clues on OPEC output. The EIA will release its short-term energy outlook report on Tuesday, the International Energy Agency’s monthly oil report is due out Friday and OPEC’s monthly report is set for release next Monday. “We remain most concerned that OPEC production continued to rise in June,” said Tim Evans, energy analyst at Citi Futures.

Given all the negative price influences on oil, Capital Economics, in a note dated Monday, lowered its end-of-2015 forecasts for Brent crude to $55 from a previous forecast of $60 and cut its outlook on WTI crude to $50 from $55 a barrel.