Pros
Great peer network within the company. Training opportunities both within XOM and outside training. XOM experience is considered good by other companies. Good opportunities for advancement (if you get very good performance reviews). Many opportunities for travel and purse strings are loose.
Cons
Advancement at XOM is based on performance ranking, and the ranking system can be influenced by how well your supervisor is respected (e.g. company politics). High rank means good raises, middle rank means very mediocre raises, low rank means ~1% raises or none. An employee's potential for management is decided very early. Those targeted as future managers are quickly advanced through key positions (assumng they don't crash/burn). Downside is those who don't get chosen typically don't advance very far. XOM is focused on grooming the next decades management as much as paying shareholders. Not much else matters.