For most of the world, the tail wind of lower oil prices is helping to lift the pace of growth.
So what happens if oil prices keep falling?
The price of a barrel of crude slipped again Thursday, with the U.S. benchmark closing just below $60—down from a summer high of about $100 a barrel. On Wednesday, the OPEC oil cartel—which for decades has sought to control prices by restricting supplies—forecast a glut of oil next year after failing recently to organize a production cutback. c
"Short term, we're seeing a U.S. economy that's growing with increasing strength, and lower energy prices are going to be a boost to consumer demand and confidence," Treasury Secretary Jack Lew said.
Read MoreLew: Lower energy prices huge boost to economy
That's because the decline is "like a tax cut to the economy," said Lew. Much like the savings you're getting at the gas pumps, lower oil prices free up cash that can be saved or invested elsewhere, helping to boost growth.
But the savings enjoyed by oil consumers are coming out of the pockets of oil-producing nations that are already feeling the pinch of an epic slide in benchmark prices.
In Russia and Venezuela, falling prices have cut revenue from oil sales, hammering local currencies, stoking local inflation and crimping economic growth. Saudi Arabia, the world's biggest exporter, has also lost billions in oil revenue, but holds a substantial cushion of cash reserves to help it ride out the price drop
Rising oil supplies are also being fed by an increase in U.S. production, slack demand from a slowing global economy and long-term efficiency gains in consuming countries.
The speed of the price drop, though, has caught most of the world by surprise.
Read MoreOil price fallout: Producers struggle as GDP grows
"Businesses and consumers to a certain extent generally expect and live in an environment where things change slowly—they make plans and they have budgets prepared ahead of time," said Greg Daco, an economist at Oxford Economics. "When you have big step shift in prices, that tends to throw off plans and budgets, especially when it happens in a matter of a few months."
As the world scrambles to adjust to cheaper oil, it remains to be seen how long—or how deep—the price drop goes. In the futures market, prices have swung widely as traders place their bets on just how low crude prices are headed.
So what happens if oil prices fall to, say, $40 a barrel? To find out, economists at Oxford Economics fired up their computer models to run projections on the growth rates of 45 economies around the world.
They started with a "baseline" forecast, pegging oil prices to an average of $84 next year, a number that, until a few months ago, seemed like a reasonable forecast.
Then they looked at several ways that oil affects growth. The list included how much oil a country produces and consumes, how big of a role oil plays in overall energy demand, the impact on currency exchange rates, fuels taxes and other factors.
Read MoreThe countries slammed worst by plunging oil prices
After knocking down the price of oil in $10 increments, the country seeing the biggest boost to growth was the Philippines, which could expect its economy to grow by 7.6 percent on average over the next two years if oil falls to $40. China and India were next in line as cheap oil beneficiaries, with growth rates of 7.1 percent and 6.7 percent, respectively
The biggest loser would be Russia—which would see growth shrink by an average 2.5 percent annually over the next two years—even without factoring in a possible currency crash and the ongoing sanctions imposed against Russia by the U.S. and Europe.
In the U.S., much of the boom in new oil supply is coming from producers that are squeezing more oil out of the ground with improved technologies like hydraulic fracking and horizontal drilling. While those techniques have breathed new life into the U.S. oil patch, they're not cheap. And a lot of the equipment and manpower needed to produce that oil has been paid for with borrowed money.
That's left some banks holding those loans—and their investors—looking closely at the increased exposure on their books to suddenly lower oil revenues. A prolonged era of low prices could also hit the broader economies of U.S. states that rely heavily on the oil industry for jobs and consumer spending.
Read MoreOil and the banks: As prices fall, risks may rise
In Europe, policymakers are struggling to revive growth and reverse a prolonged stretch of very weak inflation. The worry is that weak prices spark a bout of outright deflation—in which wages and prices begin falling, sending the economy into reverse.
That's less likely in larger economies, where the savings from lower oil prices are more widely diffused through a broader base of industries, said Daco.
"In a well-diversified economy, a rapid change will have a relatively more modest impact than an economy that's heavily focused around energy," he said
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