After years of restraining output, Opec possesses more spare crude oil production capacity than ever. The problem is, the bulk of this lies with a handful of Mideast Gulf countries whose exports are susceptible to disruption if the Israel-Iran war escalates. The sheer size of this spare capacity has still created a perception that a major supply disruption, such as the loss of Iranian exports — by far the most widely discussed scenario — could be overcome with relative ease. Together with sluggish demand growth and an anticipated surge in South American output in the second half of the year, Opec's spare capacity is limiting price spikes on the futures market. But a closure of the vital Strait of Hormuz, while considered unlikely by many oil market watchers, could decimate that restraining factor. In May, Opec's adjusted spare capacity — that is, production that could be brought on line within 30 days and sustained for at least three months — was 5.8 million barrels per day, according to Energy Intelligence's calculations. A further 900,000 b/d of adjusted spare belongs to non-Opec countries like Russia and Oman, which are cooperating with other Opec-plus members on managing supply, taking the full group's spare to 6.75 million b/d. These are historically high levels. Last year, Opec alone, excluding Iran, on average boasted a record 5.9 million b/d of adjusted spare capacity, or 1 million b/d more than the second-highest annual average in 2009. And if measuring potential spare capacity, which includes both adjusted and constrained capacity — or production that would require more than three months to bring back — then Opec-plus (excluding Iran) had 7.3 million b/d in capacity last month, Energy Intelligence estimates.