HOUSTON — The price of crude oil continued to collapse on Monday, plunging to a five-year low, as oil giants began to scale back their drilling ambitions and pare the ranks of their workers.

On the same day that the American oil benchmark traded around $63 a barrel, down more than 4 percent, ConocoPhillips announced it would cut investment spending in 2015 by 20 percent, the biggest sign yet that major oil companies are contracting.

The announcement came on the heels of BP ’s notice that it would cut middle management and other jobs in the months ahead.

Both moves suggested that the 40 percent drop in oil prices since July had spread pain beyond small exploration companies that were highly leveraged and most vulnerable to oil price swings.

“We are setting our 2015 capital budget at a level that we believe is prudent given the current environment,” said Ryan Lance, ConocoPhillips’s chairman and chief executive.

But even with the sharp cut in investments, the company projected that its oil and gas production would grow 3 percent next year because of recent start-ups of major projects in Canada, Europe and Asia, as well as increasingly productive wells being drilled in the Eagle Ford and Bakken shale fields of Texas and North Dakota.

That forecast, combined with the slow decline in drilling rigs deployed in fields worldwide, indicates that whatever hopes Saudi Arabia and other OPEC producers have that lower prices will lead to quick production declines are unlikely to happen before late 2015. The cartel decided last month to keep its 12 members’ production quotas steady, in a move that accelerated the oil price drop.

Energy experts say that more production will most likely lead to even lower oil prices, unless the economies of Europe and Asia recover more quickly than expected or if there is a major new political disruption in the Middle East or North Africa.

Wall Street analysts continued to lower their predictions of where oil prices are headed in 2015, with some projecting that global oil prices could break below even $50 a barrel — the biggest collapse since prices briefly plunged by about two-thirds during the most recent recession.

“With OPEC on the sidelines, oil prices face the greatest threat since 2009 and appear to be on track for a volatile 2015,” Morgan Stanley said in a commodity report on Monday. But the report added that “oversupply is likely exaggerated and the market may be complacent about upside risks.”

So far, the drop in oil prices has been a boon for consumers. The national average price for a gallon of regular gasoline was $2.67 on Monday, according to the AAA auto club, 27 cents lower than a month ago and 59 cents below a year ago. Energy experts say that every 10-cent drop in gasoline prices translates into a $120 in annual savings for the typical family that consumes 1,200 gallons a year.

But economists say the full consequences of the oil price drop, while positive over all, are hard to predict fully. Several oil-producing states, including Texas, Louisiana, North Dakota, Oklahoma and Alaska, are bound to be hurt since so much of their employment and tax revenue are based on oil and gas. Already in Oklahoma, monthly energy tax revenue in November declined from the year before by more than 5 percent, the first time there had been a drop in nearly two years.

And beyond the recent announcements of cutbacks, companies like ConocoPhillips are considering deferring investments in oil fields around the globe, especially in high-priced offshore and shale fields. The Norwegian oil giant Statoil has announced job cuts, and suspended or canceled rig contracts. Royal Dutch Shell and Chevron cut jobs in their North Sea operations even before oil prices plunged.

Precision Drilling, Canada’s largest oil and gas drilling contractor and a global player, announced Monday that it was cutting its capital spending next year by 44 percent.

Raymond James on Monday issued a report highlighting budget reductions of oil field service companies. “Peak to trough, we think the total U.S. rig count will decrease by 587 total rigs (or nearly 30 percent) by mid-2016,” Raymond James projected.

“In a low-price environment, investments are harder to justify,” said Michael E. Webber, deputy director of the Energy Institute at the University of Texas at Austin. Mr. Webber added that what was happening had occurred repeatedly in the oil business over the last century.

“This is what commodity markets do,” Mr. Webber said. “They go to high price, and high price inspires new production and also inspires consumers to use less. After a couple of years of that, prices collapse. Then low prices inspire consumers to consume more and encourage suppliers to turn off production. Then you get a supply shortage and prices go back up.”

Globally, economists project that countries with high fuel import bills like Japan and China should benefit from lower energy costs. China’s trade surplus soared in November to a new high because of steeply falling prices for oil and other imported commodities. India and Indonesia have already been able to shave subsidies on gasoline to reduce their burdensome fiscal deficits.

But for oil-producing countries like Russia, Venezuela, Nigeria and Iran, falling oil prices threaten their government programs, currencies and ability to pay debts. Their political stability could also be at risk. Persian Gulf countries appear to be in better shape financially to withstand plunging oil prices, but future reductions in their sovereign wealth fund global investments could hurt some financial markets.

The drop in oil prices may even hurt natural gas exporting countries since gas prices are often tied to oil prices in European and Asian markets. Along with a projected supply surge between 2015 and 2019, lower prices could jeopardize several large proposed liquefied natural gas export projects in the United States and Canada.

The Malaysian national oil company Petronas last week announced that it was delaying a final investment decision on a $36 billion liquefied natural gas project it was leading in British Columbia.

Keith Bradsher contributed reporting from Hong Kong.

A version of this article appears in print on December 9, 2014, on page B1 of the New York edition with the headline: Oil Falls to 5-Year Low, and Companies Start to Retrench. Order Reprints | Today’s Paper | Subscribe