Where America's Sulfur Comes From Now

THE WORKHORSE is a 20-minute documentary about sulfur mining and sulfuric acid, made from real archive film. It asks one question: America's last sulfur mine closed in 2000 and the acid never stopped, so where does the sulfur come from now? This page follows the film's chapters in short sections, with the chart, the data and a source for every fact.

Short answers from the film

Why did U.S. sulfur mines close?

They lost to sulfur recovered from oil and gas. Frasch mines heat huge amounts of water, so they need cheap natural gas, while refineries and gas plants recover sulfur anyway, an "involuntary byproduct" made "irrespective of sulfur demand" (USGS Minerals Yearbook 2000). Recovered sulfur passed mined sulfur in 1982 (USGS Open-File Report 02-298). The last mine, Main Pass 299, closed at the end of August 2000.

What is the Frasch process?

The Frasch process mines sulfur without digging. In Louisiana the sulfur lay about a thousand feet down, in rock on top of a salt dome. Herman Frasch sent superheated water and compressed air down a well to melt it, then pumped it up as a liquid. He first pumped sulfur late in 1894, and the process first made money in 1903 (Frasch, 1912; USGS Open-File Report 02-298).

How is sulfuric acid made?

EPA's AP-42, section 8.10 says all U.S. sulfuric acid is made by the contact process. Sulfur is burned to sulfur dioxide. Over a catalyst, the sulfur dioxide takes one more oxygen and becomes sulfur trioxide. Plants do not add that to plain water, which makes an acid mist too stable to catch. They absorb it in acid that is already 98 to 99% strong, where it forms more acid.

Where does sulfuric acid come from?

It is made from sulfur, and in the United States that sulfur now comes mostly from cleaning fuel: in 2025 about 96% of U.S. recovered sulfur came from oil refineries (USGS Mineral Industry Surveys, July 2026). About 90% of the sulfur used in the country becomes sulfuric acid (USGS Mineral Commodity Summaries 2026), and in 2023 about 80% of the sulfur in that acid went into phosphate fertilizer (USGS Minerals Yearbook 2023, Table 6).

What is the Claus process?

The Claus process is how refineries and natural gas plants turn the hydrogen sulfide they strip out of crude oil and gas into elemental sulfur. One-third of the hydrogen sulfide is burned to sulfur dioxide, and the rest reacts with that sulfur dioxide to give sulfur and water (EPA AP-42, section 8.13). Most refineries and gas plants use it, which is why American sulfur now comes from fuel, not mines.

What was Main Pass 299?

Main Pass 299 was the last sulfur mine in the United States, a Frasch mine in the Gulf of Mexico off Louisiana. It began production in 1991 at a development cost of $880 million and was more than a mile long, the largest structure in the Gulf. It closed at the end of August 2000, after low sulfur prices and a near doubling of natural gas prices, among other reasons (USGS Minerals Yearbook 2000).

Why is sulfuric acid in short supply in 2026?

Part of the answer is built in: sulfur supply cannot rise when acid makers need more. With no U.S. mine since 2000, the country's sulfur is recovered from oil and gas, an "involuntary byproduct" whose output follows fuel (USGS Minerals Yearbook 2000). The United States also imports sulfur, 53% of it from Canada (USGS Mineral Commodity Summaries 2026). The 2026 market is covered in our sulfur shortage briefing and our report on idled acid plants.

The mines closed. The acid didn't.

Sulfuric acid is made from sulfur. The American Chemical Society calls it the most-produced chemical in the world.

For most of the last century, America got its sulfur from giant mines on the Gulf Coast. The last of them closed in 2000. In 2001, for the first time since the start of the 20th century, no sulfur was made in the United States by the Frasch process (USGS Minerals Yearbook 2001).

The acid didn't stop. In 2023 the sulfuric acid sold or used in the United States still held almost 7 million metric tons of sulfur (USGS, Table 6).

Oil of vitriol, glass and lead

For centuries the acid was called oil of vitriol. In the 1740s it was made in glass globes, "the largest that could be blown with safety", so it came in small batches and it was expensive (Dictionary of National Biography).

Then John Roebuck, working with the Birmingham merchant Samuel Garbett, swapped the glass for lead chambers. The first went up in 1746. Lead holds up to the acid and can be built much bigger, and the cost fell to about a fourth (Dictionary of National Biography).

Sicily and the carusi

Cheap acid needed sulfur, and for most of the 1800s it came from one island. Until the Frasch process, 95% of the world's sulfur came from Sicily (USGS).

Miners melted the sulfur out of the rock in kilns called calcaroni, burning part of the sulfur as the fuel. The yield was about half, and the smoke poured out as sulfur dioxide (Britannica, 1911).

The ore came up on the backs of boys called carusi. The 1876 inquiry of Leopoldo Franchetti and Sidney Sonnino found them starting at age seven. The smallest carried 25 to 30 kilos, about 55 to 66 pounds, up tunnels as steep as 80 degrees (La Sicilia nel 1876).

The Sulfur War of 1840

Britain needed Sicilian sulfur for its acid. In July 1838 the government of Naples and Sicily granted a monopoly on the trade to a group of French businessmen. Prices rose, "at the expense of British interests", the House of Lords heard (Hansard, March 1840).

Britain sent the Royal Navy, which seized ships from Naples and Sicily (Hansard, June 1840). By the end of July 1840 the Foreign Secretary told the Commons the monopoly would "cease at the shortest possible period" (Hansard, July 1840).

Herman Frasch melts sulfur underground

America had sulfur of its own, but in Louisiana it sat a thousand feet down, under quicksand. A company tried to sink a shaft to it, and "the danger due to the presence of water containing hydrogen sulphide was demonstrated by the death of a number of men." The method was abandoned (Frasch, 1912).

Herman Frasch, a chemist whose day job was at Standard Oil and whose sulfur work was, in his word, "a hobby", decided not to dig at all: "the only way to mine this sulphur was to melt it in the ground and pump it to the surface in the form of a liquid." Late in 1894 superheated water went down the first well, and the man at the throttle sang out, "She's pumping" (Frasch, 1912; USGS).

That night Frasch climbed the pile alone. "It pleased me to hear the slight noise caused by the contraction of the warm sulphur, which was like a greeting from below." The next morning the mail boy told him: "Well, you pumped sulphur sure, but nobody believed it but the old carpenter, and they say he's half crazy" (Frasch, 1912). The process first made money in 1903 (USGS).

By the 1940s, a U.S. Bureau of Mines film shows, seven mines on that coast made three and a half million tons a year. They didn't bag it. They poured it into vats, where it set into walls of solid sulfur that were later blasted apart for shipping. Most of it was burned to make acid ("Sulphur", 1940s).

How sulfur becomes acid

Burn sulfur and you get sulfur dioxide. Over a catalyst it takes one more oxygen and becomes sulfur trioxide. Add water and you have sulfuric acid.

The last step has a twist. Sulfur trioxide meeting water makes an acid mist so stable that only a little of it can be caught. So plants absorb the sulfur trioxide in acid that is already 98 to 99% strong, where it combines with the water in that acid and forms more acid (EPA AP-42). You make the acid by feeding it to the acid.

You make the acid by feeding it to the acid.

The 1940s film called sulfuric acid "the workhorse of industry" and listed its jobs: glycerin, pharmaceuticals, safety glass, storage batteries, woolen clothing, photographic films, synthetic rubber, shoes, water purification, alcohol, sugar, soap and glue ("Sulphur").

Fertilizer from the sky

By that film's own count, 30% of the acid went into fertilizer ("Sulphur"). Superphosphate is made by reacting ground phosphate rock with sulfuric acid (EPA AP-42).

In New Zealand, pilots home from the war flew old Tiger Moth biplanes off farm strips to spread it on hills too steep for machines, as the 1959 film Land From the Sky shows.

Most of America's acid still goes the same way. In 2023, about 80% of the sulfur in U.S. sulfuric acid went into phosphate fertilizer (USGS, Table 6).

Tank 393, Delaware City, 2001

On July 17, 2001, a crew was repairing a catwalk above the sulfuric acid tanks at Motiva's Delaware City refinery. A spark from their hot work ignited flammable vapor in a tank of spent acid that had holes from corrosion. The tank collapsed. A contract worker, Jeffrey Davis, was killed and eight others were hurt (U.S. Chemical Safety Board).

About 99,000 gallons of acid reached the Delaware River. The Board found that an internal inspection of the tank, first scheduled for 1996, had been postponed again and again (CSB report 2001-05-I-DE). Delaware's tank-safety law now carries his name (Delaware Code, Title 7, Chapter 74A).

The Copper Basin

A century earlier, in Tennessee, the cost came as smoke. Copper miners at Ducktown roasted ore in open piles, and the sulfur dioxide killed the plants and young trees (National Register nomination). About 50 square miles were stripped, once "the largest man-made biological desert in the nation" (EPA case study).

Georgia, downwind, sued. In 1907 the Supreme Court sided with Georgia, and Justice Oliver Wendell Holmes wrote: "It is a fair and reasonable demand on the part of a sovereign that the air over its territory should not be polluted on a great scale by sulphurous acid gas" (206 U.S. 230).

The fix was to catch the gas and turn it into sulfuric acid. The first acid plant opened in 1907, and sulfuric acid became the main product of the Copper Basin (National Register nomination). The poison in the smoke became the product. The hills took longer: they were not successfully reforested until the 1980s (EPA).

The poison in the smoke became the product.

Smog and acid rain

Burning coal makes the same gas. On each day of London's great smog in December 1952, the Met Office says, 370 tonnes of sulfur dioxide turned into 800 tonnes of sulfuric acid (Met Office).

In 1974 the ecologists Gene Likens and Herbert Bormann reported rain over most of the northeastern United States averaging about pH 4 (Science, 1974). Normal rain is about pH 5.6 (EPA), so that is about 40 times more acidic.

In the Clean Air Act Amendments of 1990, Congress capped power plants' sulfur dioxide, with allowances they could trade (EPA Acid Rain Program). Many plants put in scrubbers, which turn the gas into gypsum (EPA). By 2023, sulfur dioxide from those plants was down 96% from 1990 (EPA progress report).

Scrubbers make gypsum, not sulfur. The sulfur that feeds the acid was already coming from somewhere else: out of the fuel itself.

The new source

Crude oil and natural gas carry sulfur, and refineries and gas plants have to take it out. Most use the Claus process: burn one-third of the hydrogen sulfide, and the rest reacts with it to give sulfur and water (EPA AP-42).

"So instead of mining for sulfur as was done in the early days, now sulfur, a large fraction of sulfur ... comes from petroleum refineries as a byproduct."
Semih Eser, Penn State, FSC 432 Lesson 10

The mines couldn't compete. Frasch mining needs cheap fuel to heat all that water, and natural gas was a major part of its cost. Recovered sulfur gets made anyway. The USGS calls it an "involuntary byproduct", its output set by demand for the main product "irrespective of sulfur demand" (USGS).

U.S. mined sulfur peaked in 1974 at about 8 million metric tons. In 1982, recovered sulfur passed it for the first time, and it stayed ahead every year after (Minerals Yearbook 1974; USGS).

Main Pass 299, the last mine

Main Pass 299, out in the Gulf off Louisiana, began production in 1991 at a development cost of $880 million. It was more than a mile long, the largest structure in the Gulf. It closed at the end of August 2000. Among the reasons the USGS gave: low sulfur prices, and natural gas, the fuel that heated the water, had nearly doubled in price (USGS Minerals Yearbook 2000).

By 2002 the USGS could write that "all the sulfur produced in North America is the result of environmental measures" (USGS).

Cleaner fuel, more sulfur at the refinery

Then came limits on sulfur in fuel. Highway diesel went from 500 parts per million to 15, starting in 2006 (66 FR 5002). Ships worldwide had to cut their fuel sulfur from 3.5% to 0.5% in 2020 (IMO). Mostly, that meant more sulfur pulled out at the refinery.

The film shows ship tracks, lines of cloud that form when water vapor condenses around tiny particles in ship exhaust (NASA Earth Observatory).

In 2025, about 96% of the sulfur recovered in the United States came from refineries, and most of the rest from natural gas plants (USGS).

Who makes the sulfur now

In the 1940s America shipped sulfur to the world ("Sulphur"). Today America also buys sulfur, and Canada supplies 53% of the elemental sulfur it imports (USGS). In Alberta most of it now comes out of the oil sands, and the province's stockpile stood at almost 11 million tonnes in September 2026 (Alberta Energy Regulator, ST3).

Worldwide, more than 80% of sulfur now comes from cleaning up fossil fuels (Maslin, Van Heerde and Day, 2022). And about 90% of the sulfur used in this country still becomes sulfuric acid (USGS).

The same yellow, three times

In Sicily it came up on a boy's back. On the Gulf Coast it was poured into a wall. Now it comes out of the fuel, whether anyone needs it or not. The mines closed. The acid didn't.

The mines closed. The acid didn’t.

Key numbers, with sources

• 95% of the world's sulfur came from Sicily before the Frasch process (USGS Open-File Report 02-298, 2002)
• 1894 Herman Frasch first pumps molten sulfur from a Louisiana well (USGS Open-File Report 02-298, 2002)
• 3.5 million tons a year made by seven Gulf Coast Frasch mines in the 1940s (U.S. Bureau of Mines film "Sulphur", 1940s)
• About 8 million metric tons U.S. mined (Frasch) sulfur at its 1974 peak (Minerals Yearbook 1974)
• 1982 recovered sulfur passes mined sulfur, and stays ahead (USGS Open-File Report 02-298, 2002)
• $880 million development cost of Main Pass 299, opened 1991, closed at the end of August 2000 (USGS Minerals Yearbook 2000)
• 96% drop in power-plant sulfur dioxide from 1990 to 2023, after the Clean Air Act Amendments of 1990 (EPA Power Sector Programs progress report)
• 15 ppm highway diesel sulfur limit from 2006, down from 500 ppm (66 FR 5002, 2001)
• 0.5% sulfur limit for ships' fuel from 2020, down from 3.5% (IMO, MARPOL Annex VI)
• 96% of U.S. recovered sulfur came from refineries in 2025 (USGS Mineral Industry Surveys, Sulfur, July 2026)
• 53% of U.S. elemental sulfur imports come from Canada (USGS Mineral Commodity Summaries 2026)
• Almost 11 million tonnes Alberta's sulfur stockpile in September 2026 (Alberta Energy Regulator, ST3)
• More than 80% of the world's sulfur now comes from cleaning up fossil fuels (Maslin, Van Heerde and Day, 2022)
• About 90% of the sulfur used in the U.S. becomes sulfuric acid (USGS Mineral Commodity Summaries 2026)
• About 80% of the sulfur in U.S. sulfuric acid went into phosphate fertilizer in 2023 (USGS Minerals Yearbook 2023, Table 6)

More questions

Is sulfuric acid the most-produced chemical?

The American Chemical Society calls it the most-produced chemical in the world (ACS Molecule of the Week, 2025). In 2023 the sulfuric acid sold or used in the United States held almost 7 million metric tons of sulfur (USGS Minerals Yearbook 2023, Table 6).

What happened in the Copper Basin at Ducktown, Tennessee?

Copper miners at Ducktown roasted ore in open piles, and the sulfur dioxide killed plants and young trees across about 50 square miles (EPA case study). Georgia sued, and in 1907 the Supreme Court sided with Georgia in Georgia v. Tennessee Copper Co. The fix was to catch the gas and make sulfuric acid: the first acid plant there opened in 1907, and acid became the Copper Basin's main product (National Register nomination, 1983).

What did the Clean Air Act Amendments of 1990 do about sulfur dioxide?

President George H. W. Bush signed them on November 15, 1990. They capped power plants' sulfur dioxide and let plants trade allowances under the EPA Acid Rain Program. Many plants added scrubbers, which turn the gas into gypsum, not sulfur. By 2023, sulfur dioxide from those plants was down 96% from 1990 (EPA progress report).

What is oil of vitriol?

It is the old name for sulfuric acid. In the 1740s it was made in glass globes, "the largest that could be blown with safety", so it was scarce and expensive. In 1746 John Roebuck and Samuel Garbett switched to lead chambers in Birmingham, and the cost fell to about a fourth (Dictionary of National Biography).

Does the United States still import sulfur?

Yes. In the 1940s America shipped sulfur to the world. Today it also buys sulfur, and Canada supplies 53% of U.S. elemental sulfur imports (USGS Mineral Commodity Summaries 2026). In Alberta most of it now comes out of the oil sands, and the province's stockpile stood at almost 11 million tonnes in September 2026 (Alberta Energy Regulator, ST3).

Transcript

Read the full transcript, 17 sections with timestamps

0:00 Where does the sulfur come from now?

Liquid sunshine. It pleased me to hear the slight noise caused by the contraction of the warm sulphur, which was like a greeting from below. A sulphur mine in Sicily is about the nearest thing to hell that I expect to see in this life. Sulfur used to be mined. In Sicily it was dug out and carried up by hand. In America it was melted underground and pumped to the surface. Most of it was burned to make one thing: sulfuric acid, the most-produced chemical in the world. America's last sulfur mine closed in 2000. The acid didn't stop. So where does the sulfur come from now?

0:57 Oil of vitriol, glass and lead

To answer that, start with the acid. For centuries, the acid was called oil of vitriol. By the 1740s, it was made in glass globes, only as big as a glassblower could safely blow them. So it came in small batches, and it was expensive. In 1746, in Birmingham, John Roebuck and Samuel Garbett swapped the glass for lead. Lead holds up to the acid, and it can be built much bigger. The cost of the acid fell to about a quarter.

1:34 Sicily and the child miners

Cheap acid needed sulfur, and for most of the 1800s it came from one island. Sicily. Before the American mines, the U.S. Geological Survey says 95% of the world's sulfur came from there. They melted it out of the rock in kilns called calcaroni, burning part of the sulfur as the fuel. Only about half of it came out. The smoke was sulfur dioxide. The ore came up on the backs of boys called carusi. Italian investigators in 1876 found them starting at seven. The smallest carried 55 to 66 pounds up tunnels as steep as 80 degrees. Booker T. Washington went to see them. In 1912 he wrote: I am not prepared just now to say to what extent I believe in a physical hell in the next world, but a sulphur mine in Sicily is about the nearest thing to hell that I expect to see in this life.

3:03 The Sulfur War, 1840

Britain bought about half of Sicily's sulfur to make its acid. In 1838, King Ferdinand II gave the whole export trade to one French company. And in Britain, the price doubled. In 1840, Britain sent the Royal Navy. By July, the monopoly was gone. The acid makers had already started switching to pyrite, fool's gold, which gives off the same gas when you roast it. By 1869, a chemist wrote, not more than a tenth of the acid was still made directly from sulfur.

3:43 Frasch melts sulfur underground

America had sulfur of its own. The trouble was getting to it. In Louisiana, the sulfur lay a thousand feet down under quicksand on top of a dome of salt. A New York company tried to sink a shaft to it. Gas in the groundwater killed a number of men and the shaft was abandoned. Herman Frasch was a chemist at Standard Oil and sulfur was his hobby. He decided not to dig at all. The only way to mine this sulphur was to melt it in the ground and pump it to the surface in the form of a liquid. Downward flow the superheated water and compressed air and upward comes the melted sulfur. Late in 1894, they sent the superheated water into the ground for 24 hours. Then they started the pump. More and more slowly went the engine. More steam was supplied, until the man at the throttle sang out at the top of his voice: "She's pumping!" A liquid appeared on the polished rod, and when I wiped it off, I found my finger covered with sulphur. That night, after the men had gone home, Frasch stayed. I mounted the sulphur pile and seated myself on the very top. It pleased me to hear the slight noise caused by the contraction of the warm sulphur, which was like a greeting from below. The next morning the mail boy drove him to the railroad. "Well, you pumped sulphur sure, but nobody believed it but the old carpenter, and they say he's half crazy." It took until 1903 to make money. By the 1940s, a mine like this one sent five to seven thousand tons a day into its sumps. They didn't bag it. They poured it. And there she goes.

6:11 The Gulf Coast sulfur mines

Seven mines on that coast made three and a half million tons a year, and most of it went into the fire to make acid. For most of the 20th century, this was where America's sulfur came from.

6:39 How sulfur becomes acid

Burn sulfur and you get sulfur dioxide. Add one more oxygen and it becomes sulfur trioxide. Add water and you have sulfuric acid. That extra oxygen needs a catalyst and the last step has a twist. Sulfur trioxide in plain water makes a fog of acid so stable it won't settle. So plants dissolve it in acid that's already 98% strong. You make the acid by feeding it to the acid. Sulfuric acid, the workhorse of industry. Glycerin, pharmaceuticals, safety glass, storage batteries, woolen clothing, photographic films, synthetic rubber, shoes, water purification, alcohol, sugar, soap and glue. By that film's own count, 30% of it went into fertilizer.

7:46 New Zealand's fertilizer planes

Superphosphate is phosphate rock treated with sulfuric acid, so plants can take up the phosphorus. In New Zealand, settlers had cut and burned the bush on the hills, and by 1947, the topsoil was sliding off. Grass would hold the hills, but they were too steep for machines. I'm sure we can control this erosion if we can only drop phosphate from the air. We've rigged up this hopper and we're putting it in the bomber so we can get the stuff up into the air all right, but nobody knows how it's going to come down. That lot's headed straight out to sea. We've done it. The graph we've prepared shows an almost perfect curve. Pilots home from the war bought old Tiger Moths and flew off strips on the farms. Three minutes from takeoff to takeoff. By the time this film was made, they were spreading half a million tons of fertilizer a year. Most of America's acid still goes the same way, into fertilizer, and every ton of it starts as sulfur. When the mines closed, that sulfur had to come from somewhere else. The answer starts with what all that sulfur cost.

9:38 The acid tank collapse, 2001

July 17, 2001, Motiva's refinery in Delaware City. Tank 393 held spent sulfuric acid from making high-octane gasoline, and the used acid gave off flammable vapor. A crew was welding nearby. Around 1:30 p.m., a spark from an electric arc cutting system ignites the vapor, causing a powerful explosion. The tank collapses, releasing 264,000 gallons of highly corrosive sulfuric acid. A contract worker, Jeffrey Davis, was killed. Eight people were hurt. About 99,000 gallons of acid reached the Delaware River. In 2002, Delaware passed a tank-safety law in his name. The Chemical Safety Board found that Motiva's own inspectors had repeatedly recommended an internal inspection of that tank. Motiva repeatedly postponed it. It had first been scheduled for 1996.

10:51 The red hills of the Copper Basin

A century earlier, in Tennessee, the cost came as smoke. Copper miners at Ducktown roasted their ore in open piles, burning the sulfur off as sulfur dioxide. The gas killed the plants and the young trees. About 50 square miles were left bare, what Discover magazine called the only bona fide desert east of the Mississippi. Georgia, downwind, sued. In 1907, the U.S. Supreme Court sided with Georgia. Justice Oliver Wendell Holmes wrote: It is a fair and reasonable demand on the part of a sovereign that the air over its territory should not be polluted on a great scale by sulphurous acid gas, that the crops and orchards on its hills should not be endangered from the same source. The fix was to catch the gas and turn it into sulfuric acid. The first acid plant there opened in 1907 and sulfuric acid became the main product of the Copper Basin. The poison in the smoke became the product. It would happen again on a far bigger scale. The hills took longer. In 1984, the TVA tried again, with helicopters and lime, and erosion fell from almost 200 tons per acre to eight. About a hundred acres were left bare on purpose.

12:29 Smog and acid rain

Burning coal makes the same gas. London, December 1952. Britain's weather service says that on each day of a five-day fog, 800 tonnes of sulfuric acid formed in the air over the city. In 1974, ecologists Gene Likens and Herbert Bormann reported rain over most of the northeastern United States, averaging about pH 4, about 40 times more acidic than normal rain. It was starting to affect the forest. That took a long time to become, you know, evident. For instance, the acid rain weakened some of the trees, especially the spruce trees. So at one point we had lost a whole lot of our mature spruce trees. Same thing happened with beech trees.

13:27 The 1990 Clean Air Act

This bill will cut emissions that cause acid rain in half and permanently cap them at these new levels. In 1990, Congress capped power plants' sulfur dioxide with allowances they could trade. Many put in scrubbers, which turn the gas into gypsum. By 2023, power-plant sulfur dioxide was down 96%. We still have our pollution, but pollution is now mostly car pollution. We have different issues, but the pH is wonderful. And I have to say, I give my husband credit for people who had the foresight to realize that, you know, this was a future problem, not just an immediate problem, and if it wasn't taken care of now, it would be an even bigger problem in the future. Scrubbers make gypsum, not sulfur. The sulfur that feeds the acid was already coming from somewhere else. Out of the fuel itself.

14:31 The new source

Crude oil and natural gas carry sulfur, and refineries and gas plants have to take it out. Most use the Claus process. Burn a third of the hydrogen sulfide, and the rest reacts with it to give sulfur and water. So instead of mining for sulfur, as was done in the early days, now sulfur, a large fraction of sulfur, comes from petroleum refineries as a byproduct. Why is that? Because the crude oil that is refined in these refineries becoming more sour or higher sulfur content, that should be removed because we would like cleaner fuels by environmental regulations.

15:37 Why the mines couldn't compete

The mines couldn't compete with that. Frasch mining needs cheap fuel to heat all that water. Recovered sulfur gets made anyway. The USGS calls it an involuntary byproduct. How much there is depends on how much fuel gets refined, not on who needs sulfur. U.S. Frasch production peaked in 1974. In 1982, recovered sulfur passed it for the first time, eight years before the acid rain program.

16:12 Main Pass 299, the last mine

Main Pass 299, out in the Gulf off Louisiana, opened in 1991 at a cost of $880 million, the largest structure in the Gulf of Mexico. It closed at the end of August 2000. Among the reasons the USGS gave: low sulfur prices, and natural gas, the fuel that heated the water, had nearly doubled in price. By 2002, the USGS could write that all the sulfur produced in North America is the result of environmental measures. Then came limits on sulfur in fuel to clean up engine exhaust. Highway diesel went from 500 parts per million to 15, starting in 2006. Ships worldwide had to cut their fuel sulfur from 3.5% to half a percent in 2020. Mostly that meant more sulfur pulled out at the refinery. In 2025, about 96% of the sulfur recovered in the United States came from refineries. Over 20%, approximately 750,000 gross tons is exported to foreign countries.

17:40 Canada and the yellow piles

In the 1940s, America shipped sulfur to the world. Today, America also buys sulfur and Canada supplies more than half of what it imports. In Alberta, most of it now comes out of the oil sands, and the province's stockpile stood at almost 11 million tons in September 2026. More than 80% of the world's sulfur now comes from cleaning up fossil fuels, and about 90% of the sulfur used in this country still becomes sulfuric acid. Its biggest job is the one it had in the 1940s, only bigger. Back then, the film said 30% went into fertilizer. In 2023, it was about 80%.

18:39 The mines closed

The same yellow, three times. In Sicily, it came up on a boy's back. On the Gulf Coast, it was poured into a wall. Now it comes out of the fuel, whether anyone needs it or not. The mines closed. The acid didn't. Ours is 93% technical grade. It ships from Taylor, Texas.

About this film

Sources