On campus interview, standard hour long STAR grilling. Phone interview, then onsite interview at refinery. Night before is informal dinner with engineers who recently started. Next day is for real. At least 4 45 min interviews, 3 technical, one with department head. They thoroughly vet your technical skills, project leadership experience, and overall personality type. More STAR questions thrown in. It seems to me that they are looking for type A, power driven people. Know first of all that it's a manufacturing business, then a business environment, with a little engineering thrown in.
Honestly, I didn't meet one stereotypical nerd/geek the whole day. Engineers there don't stay engineers for long. Most move on to leadership roles or business roles.
A good tip would be to have your projected career on your mind. Decide if you want technical track, management track, or business track. Stick to that the whole day. The interviewers meet at the end of the day before you go into the boss man final interview and hash you out. Above all, know yourself. If you aren't the kind of person who will fit into an environment of constant competition for your whole career, they will find out, and fast. Employees are constantly ranked versus each other on a tiered scale, with the bottom half of the tier needing remediation. It's not for the faint of heart or those who "just want to be an engineer".
All that being said, the people were pretty great. Top notch guys from MIT and all the big schools. They really get the best of the best. If that's you, and you can also deal with living in the relative crapholes these places are located in, the money is insane for someone right out of school, and the benefits sounded pretty good.