Sharks store oil in their livers primarily to stay buoyant. Unlike bony fish, sharks don’t have a gas-filled swim bladder to keep them from sinking. Instead, they rely on a massive, oil-rich liver that acts as a built-in flotation device. This liver can account for 8 to 16 percent of a shark’s total body weight, and the oils inside it are significantly less dense than seawater, giving the shark lift without requiring constant effort from its fins.
How Liver Oil Keeps Sharks Afloat
A shark’s buoyancy comes from two forces working together. The first is hydrodynamic: the shape of the body and fins generates lift as the shark swims forward, much like an airplane wing. The second is hydrostatic: the overall density of the shark’s body compared to the surrounding water. The liver is the dominant factor in that second force, and researchers have historically referred to it as the shark’s “hydrostatic organ.”
Sharks also get a small buoyancy advantage from their skeleton, which is made of cartilage rather than bone. Cartilage is lighter than calcified bone, but it’s not nearly enough on its own. The liver does the heavy lifting. Three things determine how much buoyancy it provides: the sheer mass of the liver, how much oil it contains, and the specific types of lipids in that oil.
Why Shark Liver Oil Is Uniquely Light
Not all fats float equally well. Most animals store energy as a type of fat called triacylglycerol, which has a density of about 0.92 grams per milliliter. Shark livers, especially in deep-sea species, are loaded with a compound called squalene, which has a density of just 0.86 grams per milliliter. That difference matters enormously at scale. Squalene provides roughly 80 percent more uplift per unit volume in seawater than ordinary animal fat. A second lipid commonly found in shark livers provides about 14 percent more uplift than standard fat.
Deep-sea sharks tend to have the highest concentrations of squalene because they live in environments where constant swimming to maintain depth would be energetically expensive. A liver packed with ultra-light oil lets them hover in the water column with minimal effort.
Fuel for Ocean-Crossing Migrations
Buoyancy isn’t the only reason sharks carry so much oil. The liver also serves as the body’s primary energy reserve, and sharks draw on it to power long-distance travel.
Research on white sharks has shown this in remarkable detail. Scientists tracked migrating white sharks by measuring changes in their buoyancy over time. Early in a migration, the sharks were buoyed up by full lipid reserves, drifting upward during passive glides. As the journey continued, their buoyancy steadily dropped, indicating the liver’s oil stores were being consumed as fuel. During coastal periods when the sharks were actively feeding, buoyancy remained stable, suggesting they were replenishing what they’d burned.
The pattern tells a clear story: white sharks eat and build up liver reserves near the coast, then burn through those reserves to power ocean-basin-scale migrations across open water where prey is scarce. High levels of a specific metabolic byproduct in the muscles of pelagic sharks confirm that liver fats are a primary fuel source for swimming. In a 428-kilogram white shark, the liver alone was estimated to contain about 1,425 megajoules of energy, significantly more than the roughly 867 megajoules stored in the animal’s entire muscle mass, despite muscle making up around 45 percent of body weight compared to the liver’s 12 percent. Pound for pound, the liver is a far more energy-dense organ.
The Liver as a Metabolic Hub
Beyond storage, the shark liver is the central processing plant for fat metabolism. It handles lipid synthesis, fatty acid breakdown, and the production of ketone bodies, which are molecules that other tissues can burn for energy when direct fat burning isn’t efficient. In sharks, tissues outside the liver have limited ability to break down fatty acids directly, so the liver converts stored fat into ketones and ships them out to muscles and other organs. This makes the liver not just a warehouse but an active distributor of fuel throughout the body.
Sharks accumulate liver oil through two pathways. The exogenous pathway involves digesting and absorbing fats from prey. The endogenous pathway involves the liver synthesizing new lipids internally. Both routes feed into the same massive reserve, keeping the organ primed for buoyancy and energy demands simultaneously.
Why Oil Works Better Than a Swim Bladder
Bony fish solve the buoyancy problem differently, using a gas-filled swim bladder that they inflate or deflate to rise and sink. This works well in stable depth ranges, but it comes with a serious limitation: gas compresses under pressure. A fish that dives rapidly can experience dangerous changes in swim bladder volume, and ascending too quickly can cause it to overexpand. Sharks face none of these problems. Oil is nearly incompressible, so a shark’s buoyancy stays consistent whether it’s cruising near the surface or diving hundreds of meters. This gives sharks the freedom to make rapid vertical movements without the physiological constraints that limit many bony fish.
Human Demand for Shark Liver Oil
The same squalene that keeps sharks afloat has become a valuable commercial commodity. In cosmetics, a hydrogenated form of squalene is used as an emollient and moisturizer in serums, oils, and conditioners from major brands. In medicine, squalene-based formulations are used as vaccine adjuvants, compounds that boost the immune response to a vaccine’s active ingredient. Three licensed squalene-based adjuvants are currently used in influenza vaccines, and researchers have explored them for COVID-19 vaccines as well.
This demand has real consequences for shark populations. The global squalene and squalane market is projected at $184 million in 2025, driven by cosmetics and pharmaceuticals. Intensive fishing for shark liver oil has significantly damaged deep-sea shark populations and disrupted marine ecosystems. The surge in vaccine production during the COVID-19 pandemic amplified the pressure further. The European Union now enforces strict surveillance measures to limit fishing of endangered deep-sea species and trace the origin of squalene in consumer products. Plant-based alternatives, sourced from olive oil, sugarcane, and engineered yeast, are increasingly available, though shark-derived squalene still supplies a significant share of global demand.