The theory is that there is biotic petroleum(the oil we know) formed from biomass from millions of years ago and there is abiotic petroleum that constantly forming from carbon sources deep in the Earth.

Depending on what degree of delusion, they either believe that there is more petroleum being produced than we use or there is less being produced than we need and we need to offset the deficit with other forms of energy.

As you can imagine, the believers in limitless abiotic petroleum tend to have some overlap with young Earth creationists and flat-earthers.