Taking into account what mountains are and how they appeared, I doubt there might be any oil/gas under them.

I'm not knowledgeable on the subject at all, but Wikipedia says most crude oil is composed of decayed plankton and algae. I'm guessing the mountains were never completely underwater, therefore no plankton. But its also probably too hard to expensive to drill there as well

I'm not a geologist so I can't give an answer I'd like, but I do enjoy reading about such things. Your question prompted me to search on my own about it. You should read about the formation of the Western Canada Sedimentary Basin and of course, the formation of the rockies and geologic timelines and forces involved. Wish I could actually provide a short and concise answer, but I just like to think about it and am by no means a scholar. Good luck!

Bonus edit:

Ah, so this explains the Alberta/US connection & fervor then? US always looking for oil.

Too difficult to drill that far when it’s closer to the surface.

But maybe it’s also because mountains are effectively tall barriers.

Mountains are rock all the way down so there isn't any oil under them.

OP is probably thinking of the oily mountains

Holy mountains... i like that name

too difficult to drill through the mountains?

Well, it's difficult. So why would you do it.

Unless those mountains were under water or covered in a tropical area a very long time ago, they likely wouldn’t have any oil in them because there’d be dead life forms in the sediment to get turned into oil.

Utah (the dark patch seen on your map below Idaho) has both the rocky mountains and oil because 50million years ago it was covered by lake uinta.

The question is not about doing it though. It's asking if there's oil down there...

One potential cause is that the Rocky Mountains are maybe newer than oil formation in the region? They are a pretty recent addition (around 50-80mya)

Drill, and you'll find out. Oh... wait...

I only know about this from fish YouTube so I could be wrong, but that looks like the border to the western interior seaway, a very habitable, shallow sea in north america. I think it would result in an insane algea bloom, some millions of years ago, then seal it in with seabed sediment before drying up.

rock all the way down

Their called minerals! Marie.

I don’t know anything on the topic but I have read before about seismic lines. Theres a bunch of straight lines cut through forests that are visible on google maps, and they’re apparently related to oil/gas surveying. Maybe this type of surveying requires a flatter land. Or like others said maybe theres just too much rock for oil anyway, idk.

https://cusjc.ca/mrp/fracturedforests/