@vidit12 – petroleum engineers have higher highs and lower lows – meaning when the oil markets are hot, they make much more than mechanical engineers; however when markets take a downswing, they make much less as an unemployment. Petroleum has done fantastic for the last seven years, but with the recent collapse and prices there are a lot of bankruptcies and layoffs.
Overall mechanical is steadier, however make no mistake unemployment goes up in mechanical when H1 visas increase. If you have one area that interests you a lot more than the other, then pursue that one. But if you like both equally, then think about your risk tolerance overall and whether you’d be okay going through some stretches of unemployment knowing that when the market turns back around you’ll be making a lot of money. Some people are okay with that, whereas others prefer a lower but steadier salary. Also think hard about where you want to live. The vast majority of the jobs in petroleum are going to be in Houston and Oklahoma and possibly Dallas, while mechanical is not really concentrated in any one city. If you’re from the East Coast (I am assuming given that you’re considering Penn State), consider whether you would want to live down south for job opportunities.