How much oxygen does a car burn?

Oxygen consumption compared to carbon dioxide emissions

We are all aware of our reliance on fossil fuels and their byproduct of greenhouse gases and poisons. But have you ever wondered about the oxygen needed to burn the fuel? As humanity burns more and more fuel, we are also burning more and more oxygen.

As an example of how much oxygen is being burned, we are going to use a car, but keep in mind that anything that burns fossil fuels, like coal factories, stoves, water heaters, barbecue grills, also burns oxygen. In fact, even you burn oxygen just by breathing. You might be surprised that one hour in a car burns as much as oxygen as you breathe in one month.

Cars, animals and plants all breathe air

Believe it or not, cars, animals and plants all produce energy in a similar way. When it comes to machines, it’s called combustion; and when it comes to plants and animals, it’s called respiration. Here is a simplified formula of how it works:

Fuel (sugar or petroleum) + Oxygen  →  Carbon dioxide + Water + Energy.

I discuss respiration in How much oxygen do plants (the Earth) produce? Below, we go into detail about combustion.

How much oxygen does a car burn/consume/breathe?

Below you can see an illustration that is drawn to scale. The volume of oxygen burned per gallon of gas is actually bigger than the car itself. Under ideal circumstances, a car burns 1866 times more oxygen than gasoline as measured by volume, 3.51 times as much as measured by weight, 12.5 times more as measured by molecules. The illustration below shows a cube of pure oxygen, but since only 20.95% of the atmosphere is oxygen, the actual volume of air that would be drained of oxygen is about 5 times bigger.

To make matters worse, the combustion engine is probably the most inefficient invention ever made. Poor combustion can lead to even worse pollutants being created, like carbon monoxide and even raw gas fumes. Spilled gas and pollutants still react with oxygen as if it is being burned. And, there are hidden costs. Almost all energy production burns oxygen, so the energy used to create the car itself and the transportation infrastructure also burn oxygen. So the actual amount of oxygen consumed by a car is much higher.

Here’s an analogy: The average horsepower of a car is about 200, which is the actual amount of work 200 hundred draft horses can do. The term horsepower arose when the steam engine was invented; business owners wanted to know how many horses the engine could replace. So, in a very real way, your car consumes as much oxygen as 200 horses. Imagine that the next time you drive down the road! Then imagine all the other vehicles on the highway and the number of horses that would be!

Here’s another analogy: if you were driving your car in a vacuum, like on the moon, one gallon of gas would require approximately 4 scuba tanks filled with pure compressed oxygen. A full tank of gas might need 60 scuba tanks.

Combustion engines consume more oxygen than they produce carbon dioxide

The illustration above assumes perfect conditions; however, the combustion engine is probably the most inefficient invention ever made. The explanation is multi-layered:

In a perfect world, the balanced equation for combustion looks like this:

2 C₈H₁₈ + 25 O₂ → 18 H₂O + 16 CO₂ + Δ

This means: 2 molecules of octane (pure gasoline) burned with 25 molecules of molecular oxygen (the kind of oxygen we breathe) equals the byproducts of 18 molecules of water and 16 molecules of carbon dioxide and some energy in the form of heat.

2 Gas + 25 Oxygen → 18 Water + 16 Carbon dioxide + heat energy

The average U.S. citizen consumes more than 3 metric tonnes of oxygen per month. Based on these CO2 numbers.

So, we can see that a car burns 1.56 times more molecules of oxygen than it produces carbon dioxide; meaning, we are depleting the oxygen from the atmosphere at a much greater rate than we are contributing to global warming gases. Lifeforms can use the water and carbon dioxide to grow; however, the oxygen is locked away from a breathable form. The only feasible way to release oxygen is through the complex and time-consuming process of photosynthesis. It took the Earth about 2.5 billion years to fill the atmosphere with enough oxygen to sustain life.

Adding insult to injury, the combustion engine only uses about 18%–20% of the energy to move forward. Most of the energy is lost to heat and friction, like wind resistance. Furthermore, most engines are worn out, making them even more inefficient. And most drivers accelerate and decelerate faster than needed, which burns extra fuel. All that energy then gets converted to heating the brakes. Additionally, the average vehicle emits about 3% unspent raw fuel in the exhaust, which, as I mentioned, also directly reacts with the oxygen to form pollution.

But that is not the worst part of our story: much of the oxygen burned gets bonded with pollutants, which permanently removes the oxygen from the ecosystem, meaning neither plants nor animals can use it. For example, most vehicles use fuel with an 87% octane rating. The other 13% are additives, such as: ethanol, heptane, lead and other impurities. This 13% bonds with the oxygen to create pollution like soot, carbon monoxide, sulfur and nitrogen dioxides (acid rain), and many more toxins and carcinogens.

How much oxygen does a person breathe compared to a car?

As illustrated above, a car consumes as much oxygen in one hour as the average person breathes in 33.7 days. This assumes that the car is traveling highway speeds at 70 miles per hour (MPH) with a fuel efficiency of 24.9 miles per gallon (MPG). This is the new record-breaking national fuel economy, which is for a brand new car with good fuel, traveling at average speeds and without frequent stops.

According to NASA, the average person doing an average amount of work needs 0.84 kilograms of O₂ per day (24 hours) to survive. This is the amount of oxygen the astronauts on the International Space Station use each day.

To put that into perspective: NASA estimates that humans only need 0.62 kilograms of food. So, by weight, you are actually consuming more oxygen than food.

By the way, lots of daily activities, like taking a hot shower or cooking a meal, consume almost as much energy as driving a car. 

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The bottom line

All these inefficiencies and byproducts of combustion engines have the detrimental side-effect of not only poisoning the Earth but also eroding the ecosystem’s ability to repair itself and produce the oxygen we breathe (photosynthesis). This unforeseen and unintended consequence forces humans to consume even more materials to fix the problems the pollution creates, which creates more pollution in the downward spiral of life.

In summary

The oxygen in our atmosphere is being measurably and quickly reduced. Oxygen depletion, in our opinion, will soon be recognized as the greatest crisis humanity has ever faced. And it will probably happen in our lifetime. It is critical to start changing our habits and infrastructure while we still can. Because as we all know, we can’t simply stop driving our cars tomorrow.

I recommend riding a bike. If one hour of driving a car consumes the equivalent oxygen that one person breathes in 33.7 days. Imagine how far you could ride a bike in that time!