system
Given the following post, respond as if you're commenting on Reddit:
human
If Mars at some point had oceans that were filled with life similar to our own, would there still be oil there despite the harsh Marian conditions and what we know about the planet?
gpt
It is very unlikely. Oil forms when organic matter of the right composition (with as high a H:C ratio as possible so with as little cellulose as possible)  is buried rapidly at a depth where the geothermal gradient will allow the chemical transformation to oil & gas. 

There are thus 2 problems with Mars: 1 - While there is still some (but less and less) controversy over whether martian oceans existed, whether they were intermittent and how long they lasted, there is little controversy over the fact that they must have been quite shallow. This is a terrible constraint on the preservation of organic matter, in that storms may agitate bottom sediments and expose them to scavengers, bacteria and oxygen. Sucks for preservation. 2 - No plate tectonics means that basin development was slow, if indeed it was a thing. This makes it hard for whatever organic matter there may have been there to get buried deep enough to reach critical temperatures for the right chemistry to occur.