Avantages
International travel opportunities (at least when capital projects had money to spend) and relatively quick promotion if you exhibit talent and leadership. Great salary and cushy (too cushy, really) hours for most employees.
Inconvénients
The company (as with most operators) is NOT an engineering company, and, although it employs degree-qualified engineers, does not do any serious serious engineering design work (potentially excluding some geophysics and subsurface work, where I had almost no experinece. The company is an operating company. They pay other people to do engineering, and, particularly on big projects, it shows. COP got big quite fast, and, although it has worked hard to standardize and improve its operating approach, I expect it will continue to lag the real majors.