One thing that you need to ask yourself is "Do I want to be a Pet Eng or am I interested in the Oil & Gas industry?" Either answer should point you to a path. I'm a ME and have had a heck of a career in surface facilities, compression, and downhole pumping. If you are interested in geology, rock mechanics, and geophysics then Pet Eng is a really good way to go. If you like building stuff, pipe flow, multi-phase flow, corrosion, and flow measurement kinds of things then ME might be a better way to go. There are certainly more ME's in Oil & Gas than Pet Eng guys. Many of the ME's are in petroleum jobs. Few Pet Eng are in ME jobs.
When I got out of the Navy I treated college as a job, I already knew how to drink, was married, and I'd come to grips with dealing with my hormones. I got my BS in 33 months. It is quite doable, you just have to convince your adviser that 19-24 semester hours is a fraction of the work you did in the service. I never once felt overloaded, in fact I was able to get hooked on a soap opera while in school (that really sucked when I got a job in the pre-DVR days) while maintaining a 4.0 GPA.
Getting your first job out of college, your grades matter (even though they will never matter again, they really matter for the first job) the cut off for most Major Oil & Gas companies is a 3.8 out of 4.0, second tier companies usually will look at applicants with a 3.6 (smaller companies rarely hire new grads), below that you are pretty much limited to service companies. Service companies work you to death, but at the end of 2-3 years, all of the producers are interested in you. That is really the most common path to a production company these days (when I started in 1980, the path was reversed, the service companies and smaller producers poached from the Majors--there were something like 150 engineers that started with Amoco the day I did, 10 years later there were 3 of us still with Amoco, most of the rest were doing quite well at smaller producers).
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist