I used to be a vendor to XOM as well as the majority of Big Oil in the US. I know them to be one of the most ethical and honest companies I've ever worked with. They would never allow gouging at the pump at their stations.
Most likely it'll be like todays action; Gradually up, then a pop when the rumour gets around enough, then a gradual selloff in the next severaldays after earnings announcement. That's pretty typical for most stocks. Of course, I'm assuming that they'll report decent earnings.