Yeah, oil used to be the cheapest energy source for most situations (with the notable exception of mass power generation, were coal - an environmental even worse fossil fuel - was cheaper), but over the last couple of decades due to pressure on both the supply side (the easilly and cheaply extractable stuff gone) and from competing energy sources (like solar and wind-generation) oil stopped being one of the cheapest energy sources and it was pushed into just those uses were its high energy density gave it an advantage (i.e. transportation).

With better battery technology even that advantage is being lost (so electric cars are becoming the standard), which leaves only some chemical synthesis processes as places were oil is the best option.

Coal was kind pushed out of most of its markets long ago (hence you don’t see that many steam trains around) so it is mainly used in power generation, and the falling cost of solar is making coal uncompetitive in it.

Gas is a little behind oil, with its main uses being domestic heating and cooking - now transiting to electric - and power generation - where renewables are now cheaper.

The trend for fossil fuels has been obvious for decades but there is naturally a TON of inertia in the pricing changes actually resulting in the needed infrastructure changes to transition away from them plus the Economic interests which extract rents in those areas are very literally paying politicians to delay this change as much as possible hence phenomenons like many more rightwing political parties pushing anti-renewables policies.