In my field of manufacturing, process engineers are not the highest paid. Process engineering is usually the initial title you get. You learn to tweak products brought online by somebody else. Even though small tweaks can save large amounts of money, it doesn't rate you as high on the salary scale or bonus structure as being a product engineer does. If you want to make more money, you work to get a product engineering position or an applications engineering position.
To make the most cash, go back to school, get your MBA, get a cushy sales job where you make commission on high volume parts you didn't have to work to sell ('cause that's the application engineer's job), then spend the majority of your time playing golf and forwarding all customer questions on to your already swamped process engineer 'cause hey, he's the new kid on the block and your swing needs improvement.
If you can't tell, it's been a rough past few weeks.
I'll agree with the previous two posters, it all depends on your field and where you're located. I'm in manufacturing and would make a heck of a lot more money in consulting or working for the federal gov't for that matter. Some folks in petroleum/chemical process engieering positions can make 1.5X what I do. Case in point: one of my buddies in college graduated with a degree in ChemEng with a 3.0 GPA. I graduated with a 3.75 GPA in Industrial & Systems. I started out at $15K less annually than he did, and I lived in a higher cost of living area.
It all depends.