The United States has stepped in to shield the global economy from the oil crunch triggered by the Iran war by boosting exports, selectively easing sanctions and tapping strategic reserves. This move has cemented Washington's transformation into the world's dominant energy superpower. The near-hermetic closure of the Strait of Hormuz trapped 13% of global oil supplies in the Gulf and forced Gulf producers to shut in around 9 million barrels per day of output, stripping the group of its most potent lever: spare production capacity. Saudi Arabia, the world's top crude exporter and OPEC's de facto leader, has maximized exports through its alternative pipeline route bypassing Hormuz via the Red Sea, but even that has been insufficient to offset the scale of the disruption. U.S. oil exports have surged in recent weeks, helping to temper the acute energy supply shock emanating from the Middle East. Total U.S. oil exports earlier this month hit an all-time high of 12.9 million bpd, of which refined products accounted for over 60%. Seaborne U.S. oil exports are set to climb to a record 9.6 million bpd in April, with flows to Asia nearly doubling from pre-war levels to 2.5 million bpd. For U.S. producers, the Iran war has delivered a sizeable windfall: the value of crude and refined product exports has increased by around $32 billion compared with pre-war prices, boosting both corporate earnings and tax receipts. Washington agreed in March to release 172 million barrels from its Strategic Petroleum Reserve in several tranches through 2027 as part of a coordinated global emergency drawdown of 400 million barrels. The SPR stood at around 405 million barrels by April 17, down from 415 million barrels at the start of the war – meaning the buffer against further supply shortages remains ample. Washington has also used economic sanctions as a tool to influence global energy supplies. Since March, the U.S. has selectively loosened restrictions on purchases of Russian and Iranian oil. The Trump administration on April 17 renewed a waiver allowing countries to buy sanctioned Russian oil at sea for about a month. The impact has been swift: volumes of Russian oil stored on tankers fell from a record high of more than 13 million barrels at the end of January to just 2.9 million barrels by April 24, as buyers swarmed back in. By bolstering Moscow and Tehran's revenues – even temporarily – these measures are arguably undermining broader U.S. foreign policy goals. The U.S. administration has recently backtracked on part of this strategy, not renewing a separate 30-day waiver that allowed purchases of around 140 million barrels of Iranian oil held at sea while simultaneously imposing its own Hormuz blockade to squeeze Tehran's revenues. Taken together, these measures show how the U.S. has emerged as a de facto "swing supplier." While the U.S. cannot fully replicate OPEC's role as a manager of global supply, it can respond fast and at scale. Through a combination of public policy and private market forces, Washington has eased at least some of the pain for consumers and revealed a level of market influence unmatched since OPEC's heyday. Looking ahead, the U.S. is likely to continue leveraging its export capacity and strategic reserves to stabilize markets, balancing domestic price pressures with the need to maintain strong ties with allies in Asia, Europe and Latin America who rely on U.S. oil to replace lost Middle Eastern barrels. (The opinions expressed here are those of Ron Bousso, a columnist for Reuters.) (Ron Bousso Editing by Marguerita Choy)