The Strait of Hormuz Closure Created a Refining Boom. The Question Is Whether It Lasts.

Every Thursday morning, energy traders check the same number: how many barrels of crude oil moved in or out of U.S. storage tanks that week. Analysts write about expected draws and builds. Oil futures twitch. The weekly inventory report has become a ritual.

But the ritual misses what has actually been moving the market this year.

The Strait of Hormuz — the narrow waterway through which roughly one-fifth of the world's oil supply normally flows — has been effectively closed to most shipping traffic on February 28. About 15 million barrels per day of Middle Eastern crude that used to sail through this chokepoint has been stranded. There was a ceasefire agreement announced June 15. It collapsed when the U.S. restarted the blockade on July 14. The strait remains disrupted.

The consequence has not just been higher crude prices. It has been something far more unusual, and far more consequential for investors: a historic widening of the gap between crude oil and the refined fuels made from it. That gap is what refiners get paid. And right now, the gap is at levels the industry has never seen.

The crack spread and why it matters

The profit margin for refiners is called the crack spread — the difference between the value of the gasoline and diesel they produce and the crude oil they buy as input. The standard measure, the "3-2-1 crack," values three barrels of crude against two barrels of gasoline and one of diesel.

At the start of 2026, that spread sat near $20 per barrel, compared with a 2010–2021 average of approximately $19. By mid-July, it hit a record $70. Even pulling back from that peak, it has stayed near $59, nearly tripling since January.

This is not a crude oil story. It is a refining capacity story. The Strait closure shut down millions of barrels per day of Middle Eastern refining. Ukrainian strikes on Russian refineries have knocked their crude-processing rates to their lowest level in two decades, with Russian output falling 25–30%. And in the United States, seven major refinery closures and conversions since 2019 have removed approximately 1.2 million barrels per day of U.S. crude processing capacity.

The International Energy Agency put the combined hit at 4.5 million barrels per day, or 5.4% of global refining output. That supply gap is what has pushed crack spreads and refiner margins to record territory.

What the refiners actually earned

The numbers from this year's second quarter are not incremental. They are historic.

Marathon Petroleum, the largest U.S. refiner by volume, reported record net income of $5.1 billion in Q2 2026, up from $511 million in Q1. Its refining margins doubled quarter over quarter. The company's adjusted EPS of $17.73 beat consensus of $13.73 by 27.1%.

Valero, the second-largest refiner, generated operating income of $4.47 billion in its refining segment, up from $1.27 billion in Q2 2025. It reported $5.6 billion in operating cash flow for the quarter.

The two companies combined for approximately $8.8 billion in Q2 2026 profits, beating consensus across the board. This is not a case of modestly better margins flowing through the books. It is a fundamental change in the economics of converting crude into fuel.

Over the trailing twelve months, Marathon generated $12.9 billion in free cash flow, up 254% from a year ago. Valero generated $10.1 billion, up 203%.

What the market has done

The stock market has not been slow to respond. Marathon Petroleum (MPC) trades near $399, up roughly 145% year-to-date, having nearly doubled from a 52-week low of $162. Valero (VLO) sits around $384, up about 135% YTD from a 52-week low of $155. Phillips 66 (PSX) has climbed 66%. The refining sub-industry jumped 104% in 2026, versus an 11% S&P 500 gain.

The market has rewarded the margin expansion aggressively. But the current multiples need context.

Valero trades at an EV/EBITDA of roughly 8.6x and a P/E of 15.3x on trailing earnings. Marathon is at 7.9x EV/EBITDA and 13.1x trailing P/E. These look reasonable in isolation — until you recognize the earnings they sit on top of are running at roughly 2.5 times normal levels. If margins normalize even partially, these multiples expand rapidly.

The balance sheet difference

Not all refiners are positioned the same way to weather a reversal.

Valero carries $3.5 billion in net debt against $28.3 billion in equity — a debt-to-equity ratio of 0.40. Its current ratio of 164% signals strong short-term liquidity. Marathon tells a different story: $25 billion in net debt against $25.7 billion in equity, for a debt-to-equity ratio of 1.28. Its current ratio sits at 125%.

This matters because the question isn't whether refiners will make money when margins normalize. They will. The question is how much leverage each company took on while margins were fat, and how exposed each one is when the geopolitical premium evaporates.

There is another structural difference worth noting. Marathon owns approximately 64% of MPLX, a midstream infrastructure platform that provides fee-based cash flows largely independent of commodity prices and refining margins. Valero brings operational complexity — Nelson Complexity Index of 11.5 — that lets it process heavier, cheaper crude into higher-value products, which historically provides more earnings stability as margins compress.

The reversal risk

This is where the weekly inventory story reconnects to the investment case. The EIA projects U.S. crack spreads to narrow meaningfully in the fourth quarter as summer driving demand fades. The futures market already prices in a substantial pullback: September contracts trade near $70 per barrel, while August 2027 contracts sit at $44.38, more than 35% lower.

The historical record for the refining sector at these levels of price excess is not reassuring. The S&P 500 Oil & Gas Refining sub-industry index is 41% above its 150-day moving average — a divergence that has occurred only five times. In each of those prior instances, the six-month forward return was negative, with an average decline of 10.1%.

More than that, the drivers of this rally are by nature temporary. The Strait of Hormuz closure is a geopolitical event, not a structural shift in global refining demand. A sustained ceasefire — which has been attempted twice this year — would send crack spreads sharply lower. Russian refining, damaged but not destroyed, can recover. And the U.S. has been closing refineries for years; that trend does not reverse because margins spike.

The market has priced in a world where these margins persist. The evidence from the futures curve, the historical precedent, and the fundamental nature of the supply shock all point in the opposite direction.

The investment judgment

The cash flows this year have been extraordinary. No one disputes that. The question for an investor is whether paying current prices buys durable value or captures the last lap of a margin cycle.

The weekly crude inventory report tells you what happened last week. It does not tell you whether the Strait of Hormuz will reopen, whether Russian refineries will recover, or whether a $59-per-barrel crack spread is a new normal or a temporary dislocation.

From a cash-flow perspective, both Marathon and Valero have demonstrated they can generate massive free cash flow when margins expand. Both have strong operating histories. The difference comes down to leverage — where Valero's balance sheet provides more cushion if margins compress — and structural resilience — where Marathon's midstream stake offers some insulation.

But neither of those differences changes the central fact: the earnings supporting these stock prices are running at levels driven by a supply shock that has, by its nature, an expiration date. Value investing is not about buying stocks with great current earnings. It is about buying stocks trading below their intrinsic value with a reasonable margin of safety.

At roughly 2.5x normal margins, these stocks are not trading below intrinsic value. They are trading as if the current margin environment is permanent. The margin of safety is on the other side of the trade.

While it is true that some structural capacity losses — the U.S. refinery closures, parts of the Middle East damage — may persist even after a ceasefire, the gap between today's crack spread and a normalized $20-$25 per barrel is too large for any permanent effect to fill entirely. The market has priced the best-case duration into these prices already.

The weekly inventory number will keep getting reported. It is worth watching as part of the broader picture. But the real number to watch is the crack spread — and specifically, how it moves when the geopolitical headlines shift. That is the variable that determines whether these stocks remain the best performers of the year or become the steepest decliners next year.