I was an oil and gas recruiter in Houston between 2014-2015... right on the cusp of the most recent O&G price crisis. So I graduate, watch all my engineering friends get nice fat 90k/year or even higher salaries (this is Houston equiv to ~120-130 Bay Area), start buying big trucks, big houses, spending like crazy. My candidates start doing the same, except for the oldest and most experienced, who would always warn about valleys in the field.
Lo and behold in 2014 gas prices plummets from something like 100$/barrel to 40, and suddenly almost every single one of my Chem E buddies is out of a job, and all my candidates are getting laid off, and I myself am busting my ass to keep employed because now we have maybe 2-3 jobs popping a month that get instantly targeted by every recruitment firm in the city, let alone thousands of unemployed candidates.
Anyway, one of my chem E buddies that was really good at saving money fucks off to SF to do Hack Reactor and has a great time of it. One by one more of my friends do similar, either doing a bootcamp or just jumping straight into automation type jobs. One of them even swapped to patent law. A lot of my candidates start putting things like "python" and "Matlab" on their resumes.
Long story short, the O&G industry can make you a lot of money, but it is extremely variable, and you get extremely specialized. A mech E with "rotating equipment" can't do a "static equipment job," according to hiring managers. Chem E can't do liquid natural gas jobs, even if they've got 15 years experience on all sorts of different projects. Etc. A lot of my candidates and friends just decided they'd go for a field with a lower barrier to entry and a much lower barrier for skill transfer.
(I did as well in the end)