Somebody joked recently that if Mars only had oil deposits, we'd already have cities there. Commentary on how we only ever do ambitious things if there's profit in it of course, but it got me thinking. What if Mars actually does have oil on it?
If there was ever life on Mars, even just algae and microbes in its oceans, their death and decay would have left behind a substantial quantity of oil deep underground. Most of our own oil isn't from large, complex animals (despite the nickname "dino juice") but from algae and microbes, whose biomass greatly exceeds that of more complicated, larger life forms many times over. Especially over long time periods because of how quickly they reproduce and die.
Anyways, let's say Mars does turn out to have oil deposits. Would they be valuable? You couldn't sell it to anybody on Earth because the cost of transporting it from Mars to Earth would greatly exceed the amount of money you could sell the oil for. This principle was best expressed by the saying "even if gold bricks were stacked up eyeball deep on the Moon, they couldn't be brought back at a profit".
Not by rocketry anyways. There's some possibility of using an electromagnetic mass driver to shoot ablative stone coated slugs of precious metals back to Earth where they would be collected from the crater they land in. But that's another article.
So would the oil at least be useful on Mars, for the benefit of Mars colonists? Not as a fuel for ground vehicles. Not if used in either fuel cells or internal combustion engines anyway, since both of those require an atmosphere rich in oxygen to react with the liquid hydrocarbon fuel, otherwise combustion cannot occur.
This is why there exist enormous, plentiful lakes of liquid ethane (another hydrocarbon) on the surface of Titan, but despite doubtless many meteorites striking it, they've never caught fire. That would require an oxygen rich atmosphere. Without that, you cannot use liquid hydrocarbon fuels in the way we do on Earth.
So indeed, there are already known deposits of liquid hydrocarbons in the solar system, outside of Earth. Titan is covered in it. We don't go there to retrieve it because spaceflight cannot become cheap enough to turn a profit doing that.
Even reprocessing the constituent atomic elements from burning hydrocarbon fuels back into hydrocarbon fuels using nuclear power (as some aircraft carriers can now do, to manufacture fighter jet fuel while at sea) is cheaper than harvesting those fuels from another planet or moon.
However, using nuclear power to process naturally occurring elements into something desirable is in fact one of the ways Mars colonists could benefit from oil deposits on the red planet. By refining the oil, hydrogen could be extracted, which is an important ingredient in rocket fuel.
CO2 is freely available in the Martian atmosphere, thin though it is, so the oxygen could be split out of that and used as the other major component of rocket fuel. In this way, naturally occurring oil deposits on Mars could be put to good use, making rocket fuel out of local resources.
However it's not really accurate to call that a fuel as it's not a primary energy source, and it takes more nuclear energy to make the fuel out of oil and atmospheric CO2 than you get back out of it when burned in a rocket engine. It's an 'energy storage medium'. That's fine though, it does a job we cannot currently do with nuclear power: Escaping planetary gravity wells.
There's also the fact that we need oil in order to manufacture plastics, a crucial component of space suits, habitats and basically every modern technology. The ability to make plastics and rubbers from in situ materials on Mars would be tremendously helpful to colonists.
The very real possibility that oil deposits exist deep beneath the Martian soil is, then, highly worthwhile to investigate. As yet we've sent no lander capable of drilling that deep or with the necessary sound wave based equipment to detect oil deposits, but that would be a wise inclusion on a future rover.
Stay Cozy!