The Trump administration on Tuesday ordered Chevron, already hurting from plummeting oil prices related to the coronavirus, to stop producing oil in Venezuela and halt all remaining operations there by December.

The move was Washington’s latest ratcheting up of sanctions against the socialist regime of President Nicolás Maduro, which relies on oil revenue to finance the ailing Venezuelan economy.

Chevron is the last American oil company to produce oil in Venezuela. It had hoped to continue to function there in the hope that it would have a valuable asset whenever the politics of the country stabilizes. Venezuela has the largest oil reserves in the world, although its oil industry is in shambles because of corruption, mismanagement and American sanctions.

Halliburton, Schlumberger and other American oil service companies were also covered by the tightened sanctions, although they have virtually ended their operations already.

A decline in Venezuelan oil production may make a small dent in the oversupply of oil on the world market.

Wall Street suffers its worst drop in three weeks as oil market craters.

Stocks on Wall Street fell for a second-straight day, as global markets retreated and oil prices continued their record slide.

The S&P 500 dropped more than 3 percent on Tuesday, its biggest daily decline in three weeks. Major European markets were 3 percent to 4 percent lower.

The two-day slump is yet another shift in sentiment for the stock market as it searches for a clear path forward during the coronavirus crisis.

In recent weeks, the S&P 500 soared more than 25 percent, recovering roughly half its losses from a plunge in late February and early March. Investor spirits were lifted by a federal rescue package and promises by the Federal Reserve that it stood willing to pump trillions of dollars into the financial markets.

Early signals that pace of growth in Covid-19 infections also buoyed the spirits of investors, suggesting the appearance of a dim light at the end of a tumultuous tunnel for the economy.

But periodically fresh evidence of the scale of the downturn — more than 20 million jobs have disappeared in the United States in four weeks — has pierced the bubble and returned the focus to the sheer size of the recession.

The red flags have come in the form of prominent forecasts about collapsing corporate earnings, or a contraction in G.D.P. that would have been unthinkable before the outbreak. (Goldman Sachs expects the economy to shrink at an annualized pace of 34 percent in the second quarter.)

This week, it came from the oil markets, as the price of one oil benchmark dipped below zero for the first time, meaning some holders were ready to pay people to take a barrel off their hands.

"Every so often, reality bites," said Steve Sosnick, chief strategist at Interactive Brokers in Greenwich, Conn. "You could not ignore what was going on in the oil markets."

The unnerving inversion in oil prices reflected an economy in free-fall, disappearing demand for petroleum, and the fact that there are few places left to store all the crude still being pumped.

On Tuesday the sell-off in oil continued, with the most closely watched price for oil in the United States, for a futures contract stipulating delivery of West Texas Intermediate crude in June, plunging to $11.69 a barrel, well away from negative territory but still down by nearly half. Brent crude, the global benchmark, also cratered.

Shares of some oil producers, however, rose on Tuesday after President Trump said on Twitter that he was asking administration officials to "formulate a plan that will make funds available" to help the industry.

The Trump administration is stepping up pressure on some businesses and institutions to return emergency small-business loans that they took if they already have access to capital or face "severe consequences."

Shake Shack and Harvard University have been under fire this week for taking millions of dollars of stimulus money that was meant to help small businesses cope with the coronavirus pandemic. With Congress set to replenish the Small Business Administration’s Paycheck Protection Program this week, the White House is planning to update its guidance to ensure that rich organizations do not take money that they do not need.

"Harvard’s going to pay back the money," President Trump said at a news conference on Tuesday.

Harvard, which has a $40 billion endowment, received $8 million in loan money. Shake Shack said this week that it would return its $10 million loan after a public uproar.

Treasury Secretary Steven Mnuchin said it appeared that there was some ambiguity in the rules surrounding the loan program that made big companies think they were allowed to apply for the loans.

"The intent of this was for businesses that needed the money," Mr. Mnuchin said. "The intent of this money was not for big public companies that have access to capital."

Mr. Mnuchin said that the Treasury Department would release new guidance explaining the certification requirements for the loans and that companies that did not meet those requirements would have the opportunity to return the money. Those that fail to do so will face "severe consequences," Mr. Mnuchin said without elaborating on what the penalties would entail.

General Motors shuts down Maven, its car-sharing service.

General Motors said on Tuesday that it was shutting down its four-year-old car-sharing service, Maven, the latest such venture to close its doors.

Maven, which allows customers to rent cars by the hour, has struggled to build a substantial following. It was forced to suspend services in March because of the coronavirus outbreak.

"We’ve gained extremely valuable insights from operating our own car-sharing business," Pamela Fletcher, G.M.’s vice president for global innovation, said in a statement. "Our learnings and developments from Maven will go on to benefit and accelerate the growth of other areas of G.M. business."

G.M. has used Maven to test several types of businesses. For a time, it tried parking fleets of cars at apartment buildings and making them available to residents for small fees. It also tried providing cars to drivers working for delivery services such as GrubHub.

Automakers had hoped car-sharing would evolve into a new line of business that provided transportation as a service, attracting an increasing number of younger consumers who prefer not to own cars themselves. The business was intended to compete with ride-hailing companies like Uber and Lyft, and more established car-sharing services such as ZipCar.

But efforts by auto manufacturers have failed to take off. BMW and Daimler both introduced their own car-sharing companies in the United States, then combined them, before closing the operations down last year. Ford operated a ride sharing service aimed at San Francisco area commuters but also gave up on the venture.

An oil market meltdown like we’ve never seen is getting worse.

A bust in the oil market worsened on Tuesday as traders were gripped by fear that crude output remains far too high and storage is quickly running out.

On Monday, the futures contract for West Texas Intermediate crude to be delivered in May, fell into negative territory — a bizarre move that has never before happened. In other words, some traders were willing to pay buyers to take oil off their hands.

But other benchmarks of the price of crude had remained much higher (closer to $20 per barrel), suggesting that the negative price was partly a result of how oil is traded, with different prices set for crude that will be delivered at different points in time.

On Tuesday, the rest of the oil market also crashed. The West Texas Intermediate contract for June delivery fell 43 percent to $11.69 a barrel, and Brent crude, the international benchmark, was down about 21 percent.

Demand for oil is disappearing, and despite a deal by Saudi Arabia, Russia and other nations to cut production, the world is running out of places to put all the oil being pumped out — about 100 million barrels a day. At the start of the year, oil sold for more than $60 a barrel.

Refineries are unwilling to turn oil into gasoline, diesel and other products because so few people are commuting or taking airplane flights, and international trade has slowed sharply. Oil is already being stored on barges and in any nook and cranny companies can find. One of the better parts of the oil business these days is owning storage tankers.

"I’m just living a nightmare," said Ben Sheppard, president of the Permian Basin Petroleum Association, which represents shale oil companies in the area of Texas and New Mexico that became the world’s largest oil field last year.

The sell-off in oil sharpened after the Texas Railroad Commission declined on Tuesday to force oil producers in the state to cut production. While one commissioner wanted to cut production by 20 percent, the other two members of the commission said they needed more legal advice before acting. The commission used to regularly manage oil production but hasn’t done so since the early 1970s.