"Well, the nice thing about Google is it's different every month. This is all different from when I wrote this blog post a month ago. If you go to the Google+ page for the business (listed in the search listings next to "Write a Review"), you get the Contact Info pane. From there, click Edit Details. I think you can "Report something else" and then "Add a missing place" and add a Gas Station under category, but you have to enter a place name and address." - Phil Windley