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

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

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)

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

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 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.

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/

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

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

too difficult to drill through the mountains?

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