I'm not sure if you mean the gas was diluted/had an additant/was mislabeled or of the wrong type and it does make a difference as to coverage.
If YOU accidentally put diesel in a gas tank (or vice versa) you need to look at your comprehensive coverage to see if it's covered or not. Coverage would in part depend on your state's regulations. Most insurance coverage that I'm aware of would at least cover the hotel stay and possibly this might show up in your S+B policy as opposed to vehicle insurance.
If the gas station is at fault due to mis-labelling/employee error, etc. your insurance company should go after their insurance company to be made whole or depending on your state, you should.
HTH
