Oil futures finished booked a fourth straight decline in a row, wrapping up at the lowest in more than three months, on heightened concerns for the global economy and tariff tensions that could both potentially hurt demand for oil. Oil extended their losses for the session into electronic trading late Monday, with U.S. prices heading into bear-market territory.

In electronic trading late Monday afternoon, WTI was at $52.74. A settlement at or below $53.04 for the front-month would mark its entry into a bear market, according to Dow Jones Market Data, defined as a drop of 20% or more from its recent high. It’s most recent high was $66.30 on April 23. August Brent lost 71 cents, or 1.2%, to finish Monday at $61.28 a barrel on ICE Futures Europe. That was the lowest front-month contract settlement since Jan. 28. WTI lost nearly 8.8% last week and plunged 16.3% for May, according to Dow Jones Market Data. That was the worst monthly loss since November, when it skidded 22%. Meanwhile, front-month contract prices for Brent slumped 11.4% month to date and wrapped up the week off 6.1%.

Most of the movement for oil has been based on “economic concerns of weakened growth because of the potential impact of [the] trade situation,” said James Williams, energy economist at WTRG Economics. U.S. tariffs on Mexican goods have added to the concerns about China, he said. The market has primarily been stricken by growing fears that trade clashes between the U.S. and its international counterparts will weaken economic output in an already fragile world, thereby hurting appetite for crude. On Friday, worries about slack in demand for crude were heightened after Trump unexlectedly announced the tariffs on good from Mexico in a tweet late Thursday.

Meanwhile, Saudi Energy Minister Khalid al-Falih has called recent volatility “unwarranted” and has said he expects OPEC to help to stabilize prices beyond the end global output pact that ends at the start of July. “We have previously stated our commitment to do whatever it takes to stabilize markets and we have delivered on those promises. And I am making that commitment again,” he said, according to reports. Traders have also been weighing expectations for the production-cut agreement between the Organization of the Petroleum Exporting Countries and their allies ahead of the deal’s expiration at the end of this month, said Williams. “The price crash last week virtually guarantees the production cuts will be extended.” The next OPEC meeting, which had been scheduled for June 25-26, may be postponed to early July at the request of Russia, according to some news reports. Meanwhile, the “strength of Iran sanctions” seems to be “a little weaker than a week or two ago,” said Williams.