I stopped buying fuel from exon after they dodged responsibility for the Valdez oil spill. Sadly I must buy again because my work gas card is Exxon only.
This app is a great idea in theory so I can find fuel when Im in unfamiliar areas. However you cannot rely on any of the details to be correct. For example I need diesel fuel. Stations which claim to have diesel sometimes do not. This app will find you Exxon stations but dont count on the details. Call ahead if you need something special.
Update 8/2014: today, once again, I trusted this app to direct me to a station with diesel. When I arrived, there was only gasoline. Never neglect to call ahead if you have any specific needs.