Indeed they are. In fact, I filled up at one earlier today. Though there is only one refinery in TX—Deer Park.
Again—does the strike begin to explain the sudden jump in gas prices?
Currently about 15% of the US refining capacity is affected.
Remember this, for discussion's sake, let's say all Shell and BP gas stations closed because of the strikes, all the other brands would have to take up additional load.
All the independent gas companies who get their gas from BP, might have to get it from somewhere else.