That leaves the higher-cost producers, and the service companies that drill for them, most immediately vulnerable. Diamondback Energy, a medium-size company based in Texas, slashed its 2020 production plans, cutting the number of hydraulic-fracturing crews to six from nine. Other companies are expected to follow suit in the coming days.

The operations in greatest jeopardy are small, private ones with large debts, impatient investors and less productive wells. Small companies — those with a couple of hundred wells or fewer — account for as much as 15 percent of American output, which has more than doubled over the last decade to roughly 13 million barrels a day.

But medium-size companies are also imperiled, including Chesapeake Energy, according to Morgan Stanley. Chesapeake, a major Oklahoma oil and gas company, has $9 billion in debt and little cash because of persistently low commodity prices.

Chesapeake did not immediately respond to requests for comment.

In an investment note on Monday, Goldman Sachs said that large companies like Chevron and ConocoPhillips would be prepared to handle the shock, but that Exxon Mobil could be forced to cut spending on exploration and new production, which has recently been focused on West Texas, New Mexico and the waters off Guyana.

Shares of Occidental Petroleum, deeply in debt from its acquisition of Anadarko last year, declined by more than 50 percent over concern that it would need to slash its dividend.