A century ago, crude oil was the most valuable substance on the planet, but exploration and innovation have made it far less expensive. Today, it's eclipsed in value by the likes of gold, diamonds, and even Caterpillar fungus (you read that correctly).

There are many other obscure materials you’ve probably never heard of that command a premium price because they’re ultra-rare, hard to extract, or valued for unique properties. Read on to discover the most valuable legal substances on Earth (and beyond in one instance) right now. 

All dollar amounts in US dollars. Prices correct as of May 2024.

It might seem odd that raw fish eggs are among the most illustrious and expensive substances in the world, but gourmands will tell you there's no better taste. Iranian beluga caviar is the costliest caviar in the world, with 50 grams of the most expensive variety of the luxury light bite recently selling for around $635 (£550) for 125g at London's speciality food retailer, Notting Hill Fish & Meat Shop. That equates to about $5.60 (£4.40) per gram or $158 (£124) per ounce.

The beluga, the fish from which this rare caviar is produced, typically takes 10 years to begin producing eggs and is now extremely rare due to overfishing.

One of the most expensive garnishes in the world is the wonderfully aromatic saffron. This sultry spice, extracted from crocus flowers, is used in a variety of ways. Saffron is used as a colouring agent, for seasoning, to scent rice, and also as a natural remedy to combat everything from depression to menstrual cramps.

Its subtle taste and medicinal properties make saffron one of the most sought-after substances on the planet. Online estimates suggest saffron can retail for anything between $10 and $20 (£7.80-£15.70) per gram, while British saffron company The Cheshire Saffron currently sells 1g tins for £20, which works out to around $25.

This silvery-white metal is one of the rarest metals in the world. It's a key component in catalytic converters, which are found in car exhausts, and is normally in high demand. More than 80% of palladium is used in this way, but the metal is also used in jewellery, where it's sometimes referred to as "white gold".

During the pandemic, palladium outperformed gold – and prices have more recently surged due to the Russian war in Ukraine. Russia is the world's largest palladium producer and global sanctions have disrupted its exports, causing the price of the metal to hit an all-time high of $3,435.50 (£2.6k) per ounce on 7 March 2022, according to Currency.com. That worked out at around $121 (£91.50) per gram.

According to BullionVault, the current price is around $32.31 (£25) per gram or $1,004.89 (£789) per ounce, so prices have dropped considerably.

Platinum is a metal that's highly sought after for jewellery, but it has a multitude of other uses too. Platinum is used in laboratory equipment and even in anti-cancer drugs.

Many precious metals lost value due to the pandemic as uncertain markets caused investors to trade in investments for hard cash. Platinum prices plunged by 40% between February and March 2020 as the pandemic struck, according to Reuters, but the price has since bounced back. It now sits at around $33.61 (£26) per gram, or $1,045 (£821) per ounce, according to BullionVault. 

Sperm whale vomit may not be at the top of your wishlist, but this highly prized substance can command staggering prices. Ambergris has had various uses throughout history, most notably in the high-end perfume industry – as it ages, the unpleasant-looking matter develops a fragrant smell. 

Today, it's illegal to buy, sell, or profit from ambergris in many parts of the world, as sperm whales are under protection. But online estimates suggest ambergris is typically valued at around $35 (£28) per gram, making it one of the most expensive substances on Earth.

Although revered by everyone from ancient Aztec tribes to chart-topping hip-hop MCs, gold is much more than a shiny metal that exudes an image of wealth. Gold can be used as an electrical conductor, or even eaten in the form of gold leaf, and it remains one of the most expensive substances on Earth.

In times of crisis such as the COVID-19 pandemic and the conflict in Ukraine, analysts are quick to check what happens to the price of the precious metal as it's seen as a safe investment. But while the price of gold was initially boosted in 2020, peaking at $66.46 (£52.60) per gram on 6 August, it then started to drop off as the initial panic faded. In fact, it lost more than 10% of its value since those highs. However, ongoing global instability has meant gold is now priced at $76.94 (£60) per gram, or $2,392.98 (£1.8k) per ounce, according to BullionVault. 

The word "fungus" doesn't typically suggest something of high value, but a hybrid caterpillar fungus that lives in and kills caterpillars can sell for up to three times its weight in gold. This carnivorous fungus is the world's most expensive parasite, and it only appears for a couple of weeks each year in remote parts of Nepal, India, Tibet, and Bhutan. It's been a key ingredient in Tibetan and Chinese medicines for centuries, and its scarcity and the difficulty of obtaining it mean that a single gram can sell for anywhere between $30 and, albeit rarely, $110 (£24-£87). That works out at a maximum of $3,125 (£2.5k) per ounce.

The fungus is such a money-maker that experts believe up to 80% of household income in the Tibetan Plateau and Himalayas comes from selling the parasite.

Another rare and valuable precious metal is rhodium, which is currently the most expensive metal in the world. Similar to palladium, this silvery-white and hard corrosion-resistant metal is mainly used in the manufacturing of catalytic converters (pictured). However, rhodium has qualities that make it even more desirable to car manufacturers as the metal is better at removing nitrous oxides from vehicle fumes and is easier to install in existing converters.

The demand for rhodium by the automotive industry initially dropped as a result of the pandemic, and so did its value. But it's since bounced back and now commands a price of $4,825 (£3.8k) per ounce according to moneymetals.com, meaning that a gram of rhodium would set you back around $155 (£122).

Iridium is a by-product of nickel and copper production and is a dense, silvery-white metal. It’s the most corrosion-resistant metal on the planet and is routinely used as a hardening agent for platinum alloys. You'll find it in pen tips and compass bearings, and it's used to make crucibles in very hot temperatures.

The reason it’s so expensive at $4,800 (£3.7k) per ounce, or about $171 (£134) per gram, according to figures from dailymetalprice.com, is because it's one of the rarest elements found in the Earth's crust.

You might be surprised to learn that several types of venom can fetch a small fortune. One of the priciest is coral snake venom, which is favoured for its antiviral and antibacterial properties, and is priced at an astonishing $4,000 (£3.1k) per gram or $113,400 (£89k) per ounce.

Coral snakes have the second-strongest venom of any snake after the black mamba and are recognisable by their vibrant colours.

If you're thinking of building a nuclear reactor or weapons of mass destruction, plutonium is the key ingredient that you can’t do without. Priced around the same as coral snake venom, prices range up to $4,000 (£3.1k) per gram for pure-grade plutonium – equivalent to nearly $113,400 (£89k) per ounce.

This radioactive chemical is only found today in trace amounts of uranium, which makes it a rare and sought-after substance. 

Taaffeite gems are a million times rarer than ordinary diamonds and can cost around $2,500 (£2k) per carat (0.2 grams), which works out as $12,500 (£9.8k) per gram or $354,400 (£279k) per ounce. Although they can be immensely difficult to find, they're typically used in ultra-expensive jewellery.

You may never have heard of it, but Soliris is a highly valuable drug used to treat an ultra-rare disease called Atypical Haemolytic Uraemic Syndrome (aHUS). It’s also one of the most expensive drugs in the world, costing a jaw-dropping $6,830 (£5.4k) for a 300mg vial, which equates to $22,767 (£17.9k) per gram or about $637,476 (£501k) per ounce.

In 2017, the Patented Medicine Prices Review Board ruled that Alexion, the pharmaceutical company that produces Soliris, sold the drug at an excessive price from 2009 to 2015. 

Tritium is a radioactive form of hydrogen, also known as an isotope, that's produced naturally in the upper atmosphere when gases and cosmic rays collide. When you see the self-illuminating "EXIT" signs in public buildings, tritium creates that luminescent glow.

It’s highly unlikely that you'll ever need tritium, but if you do, a gram is more expensive than many new cars at $30,000 (£23.6k). That's equivalent to $850,500 (£668k) per ounce.

With the rarest varieties costing up to $8,500 (£6.7k) per carat – about $42,500 (£33.4k) per gram or around $1.2 million (£943k) per ounce – the Benitoite blue gemstone is one of the rarest substances known to humankind.

Formed in the late cooling stages of a hydrothermally altered serpentinite, Benitoites are found in San Benito County in California and are some of the most striking and glittery gems on the planet. 

Red beryl is one of the world’s rarest gemstones. To give you an idea of how rare it is, one red beryl crystal is found for every 150,000 gem-quality diamonds.

One carat (0.2 grams) of red beryl can cost up to $10,000 (£7.9k) for top specimens, according to gem company GemSelect. The precious stone costs around $50,000 (£39.3k) per gram, or $1.42 million (£1.1m) per ounce. The stone can only be found in tiny quantities at three sites in the world in Utah and New Mexico.

When it comes to rare and expensive gemstones, not many can match the exquisite and unique serendibite inosilicate mineral. Initially discovered in Sri Lanka in 1902, and more recently in Myanmar, this rare mineral can cost in the region of $18,000 (£14.1k) per carat – equivalent to $90,000 (£70.7k) per gram or $2.55 million (£2m) per ounce.

Some estimates suggest prices could be much higher, even reaching $2 million (£1.6m) per carat. With a complex chemical makeup, this much sought-after inosilicate is mainly used in ultra-expensive jewellery.

According to jewellery industry magazine National Jeweler, a grandidierite gem weighing 4.96 carats (almost one gram) and on display at the Wilensky Exquisite Mineral Gallery in New York was priced at $129,500 (£102k) in 2019. That makes an ounce worth about $3.67 million (£2.9m). 

The rare gemstone was discovered in 1902 in Madagascar. Clear and facet-grade grandidierite stones are some of the hardest gems to find.

Diamonds are said to be a girl’s best friend – but they're a bank manager’s, too. Although the price of a diamond heavily depends on its quality and cut, a pure one-carat diamond typically ranges from $2,000 (£1.6k) to $16,000 (£12.6k). This equates to $10,000-$80,000 (£7.9k-£62.9k) per gram. 

Although many people believe that the massive price tag is because of the scarcity of diamonds, the truth is that not all diamonds are rare. But the rarer ones are more expensive, costing up to $26,950 (£21.2k) per carat, $134,750 (£106k) per gram, or $3.8 million (£2.9m) per ounce.

Painite is one of the rarest borate minerals in the world. It was first discovered by and named after British mineralogist Arthur CD Pain, who originally thought it was sapphire. The mineral comes from Myanmar and there are thought to be approximately 1,000 painite crystals in circulation.

Because its so rare, a single carat (0.2 grams) of Painite can cost $60,000 (£47k), making a gram worth $300,000 (£236k) and an ounce worth a staggering $8.5 million (£6.7m). It's mainly used for ultra-lavish engagement rings.

Although we've already mentioned diamonds, it's important to point out that red diamonds are the rarest stones on the planet and can cost in the region of $1 million (£785.6k) per carat (0.2 grams). That makes a gram worth $5 million (£3.9m) and an ounce worth $142 million (£112m).

There are fewer than 30 red diamonds known to humankind, most of which weigh less than half a carat. The largest red diamond ever found was 5.11 carats in size and was sold for $8 million in 2011, the equivalent of $11.2 million (£8.8m) in today's money.

You might have heard the term "designer drugs", but "designer chemicals" are also a massive business. Californium 252 is a special isotope that's used to find the layers of water and oil in oil wells. This synthetic radioactive element has a half-life of 2.645 years and is produced by nuclear reactors.

The chemical was first made in 1950 at Berkeley in California and can cost a jaw-dropping $27 million (£21.2m) per gram, or $765 million (£601m) per ounce.

Its name doesn't exactly roll off the tongue, but the scientists behind "Nitrogen Atom-Based Endohedral Fullerenes" believe it could change the future of technology.

Designer Carbon Materials in Oxford, UK claims this newly developed material – which it describes as "essentially a minuscule cage of carbon atoms, with a nitrogen atom inside" – could be used to create tiny atomic clocks, which measure the passing of time by monitoring the frequencies of atoms. At present, atomic clocks can be as big as a whole room, but this powder could make alternatives that are small enough to fit in a smartphone. 

A quantity of Nitrogen Atom-Based Endohedral Fullerenes was recently sold for £110 million ($140m) per gram, which works out to around £3.08 billion ($2.4bn) an ounce. It's been billed as "the most expensive thing on Earth". But incredibly, there's one more item on our list – and it costs 44,000 times as much...

When it comes to finding the most expensive substance known to humankind, nothing else comes close to antimatter. If you thought this substance only existed in science fiction, think again. Back in 1999, NASA scientists predicted it would cost $62 trillion (£49tn) to make a gram of antimatter. They were almost exactly right: today, the price tag is around $62.5 trillion (£49tn) per gram, according to Steven Farmer, author of Strange Chemistry. That's equivalent to around $1,772 trillion (£1.4tn) per ounce. 

Some say that in the years to come, this special substance will fuel intergalactic space travel, but for now, that does remain in the realm of science fiction... 

Read more: What are critical minerals and who's winning the race to control them?