In early June, at the behest of the Biden administration, German leaders assembled top economic officials from the Group of 7 nations for a video conference with the goal of striking a major financial blow to Russia.

The Americans had been trying, in a series of one-off conversations last year, to sound out their counterparts in Europe, Canada and Japan on an unusual and untested idea. Administration officials wanted to try to cap the price that Moscow could command for every barrel of oil it sold on the world market. Treasury Secretary Janet L. Yellen had floated the plan a few weeks earlier at a meeting of finance ministers in Bonn, Germany.

The reception had been mixed, in part because other countries were not sure how serious the administration was about proceeding. But the call in early June left no doubt: American officials said they were committed to the oil price cap idea and urged everyone else to get on board. At the end of the month, the Group of 7 leaders signed on to the concept.

As the Group of 7 prepares to meet again in this week in Hiroshima, Japan, official and market data suggest the untried idea has helped achieve its twin initial goals since the price cap took effect in December. The cap appears to be forcing Russia to sell its oil for less than other major producers, when crude prices are down significantly from their levels immediately after Russia’s invasion of Ukraine.

Data from Russia and international agencies suggest Moscow’s revenues have dropped, forcing budget choices that administration officials say could be starting to hamper its war effort. Drivers in America and elsewhere are paying far less at the gasoline pump than some analysts feared.

Russia’s oil revenues in March were down 43 percent from a year earlier, the International Energy Agency reported last month, even though its total export sales volume had grown. This week, the agency reported that Russian revenues had rebounded slightly but were still down 27 percent from a year ago. The government’s tax receipts from the oil and gas sectors were down by nearly two-thirds from a year ago.

Russian officials have been forced to change how they tax oil production in an apparent bid to make up for some of the lost revenues. They also appear to be spending government money to try to start building their own network of ships, insurance companies and other essentials of the oil trade, an effort that European and American officials say is a clear sign of success.

“The Russian price cap is working, and working extremely well,” Wally Adeyemo, the deputy Treasury secretary, said in an interview. “The money that they’re spending on building up this ecosystem to support their energy trade is money they can’t spend on building missiles or buying tanks. And what we’re going to continue to do is force Russia to have these types of hard choices.”

Some analysts doubt the plan is working nearly as well as administration officials claim, at least when it comes to revenues. They say the most frequently cited data on the prices that Russia receives for its exported oil is unreliable. And they say other data, like customs reports from India, suggests Russian officials may be employing elaborate deception measures to evade the cap and sell crude at prices well above its limit.

“I’m concerned the Biden administration’s desperation to claim victory with the price cap is preventing them from actually acknowledging what isn’t working and taking the steps that might actually help them win,” said Steve Cicala, an energy economist at Tufts University who has written about potential evasion under the cap.

The price cap was invented as an escape hatch to the financial penalties that the United States, Europe and others announced on Russian oil exports in the immediate aftermath of the invasion. Those penalties included bans preventing wealthy democracies from buying Russian oil on the world market. But early in the war, they essentially backfired. They drove up the cost of all oil globally, regardless of where it was produced. The higher prices delivered record exports revenues to Moscow, while driving American gasoline prices above $5 a gallon and contributing to President Biden’s sagging approval rating.

A new round of European sanctions was set to hit Russian oil hard in December. Economists on Wall Street and in the Biden administration warned those penalties could knock oil off the market, sending prices soaring again. So administration officials decided to try to leverage the West’s dominance of the oil shipping trade — including how it is transported and financed — and force a hard bargain on Russia.

Under the plan, Russia could keep selling oil, but if it wanted access to the West’s shipping infrastructure, it had to sell at a sharp discount. In December, European leaders agreed to set the cap at $60 a barrel. They followed with other caps for different types of petroleum products, like diesel.

Many analysts were skeptical it could work. A cap that was too punitive had the potential to encourage Russia to severely restrict how much oil it pumps and sells. Such a move could drive crude prices skyward. Alternatively, a cap that was too permissive might have failed to affect Russian oil sales and revenues at all.

Neither scenario has happened. Russia announced a modest production cut this spring but has mostly kept producing at about the same levels it did when the war began.

Fatih Birol, the executive director of the International Energy Agency, has called the price cap an important “safety valve” and a crucial policy that has forced Russia to sell oil for far less than international benchmark prices. Russian oil now trades for $25 to $35 a barrel less than other oil on the global market, Treasury Department officials estimate.

“Russia played the energy card, and it didn’t win,” Mr. Birol wrote in a February report. “Given that energy is the backbone of Russia’s economy, it’s not surprising that its difficulties in this area are leading to wider problems. Its budget deficit is skyrocketing as military spending and subsidies to its population largely exceed its export income.”

Biden administration officials say that there is no evidence of widespread evasion by Russia, and that Mr. Cicala’s analysis of Indian customs reports does not account for the rising cost of transporting Russian oil to India, which is embedded in the customs data. A White House official told reporters traveling with Mr. Biden in Hiroshima on Thursday that the Group of 7 leaders would adopt new measures meant to counter price-cap evasion in their meeting this weekend.

There is no dispute that the world has avoided what was privately the largest concern for Biden officials last summer: another round of skyrocketing oil prices.

American drivers were paying about $3.54 a gallon on average for gasoline on Monday. That was down nearly $1 from a year ago, and it is nowhere near the $7 a gallon some administration officials feared if the cap had failed to prevent a second oil shock from the Russian invasion. Gas prices are a mild source of relief for Mr. Biden as high inflation continues to hamper his approval among voters.

After rising sharply in the months surrounding the Russian invasion, global oil prices have fallen back to late-2021 levels. The plunge is partly driven by economic cooling around the world, and it has persisted even as large producers like Saudi Arabia have curtailed production.

Falling global prices have contributed to Russia’s falling revenues, but they are not the whole story. Reported sales prices for exported Russian oil, known as Urals, have dropped by twice as much as the global price for Brent crude.

The Group of 7 leaders meeting in Japan this week will probably not spend much time on the cap, instead turning to other collective efforts to constrict Russia’s economy and revenues. And the biggest winners from the cap decision will not be at the summit.

“The direct beneficiaries are mostly emerging market and lower-income countries that import oil from Russia,” Treasury officials noted in a recent report.

The officials were referring to a handful of countries outside the Group of 7 — particularly India and China — that have used the cap as leverage to pay a discount for Russian oil. Neither India nor China joined the formal cap effort, but it is their oil consumers who are seeing the lowest prices from it.