You would be really shocked to know that Exxon and Chevron among others actually maintain the pipes. I have been personally on site when they show up and monitor the pipe for leaks. They also prod and poke to physically to monitor if there is any movement underground and mark the pipelines as to nobody drills within a certain distance.
Seen it with my own eyes. Sad thing, Exxon came out and dropped in on a helicopter once just to stake out the pipe.