There is a petrol station less than a kilometer after going thru the saudi border from qatar (right side). There is another one a few kilometers before exiting saudi to the UAE (left side).

There is a petrol station a few kilometers after passing thru the UAE border (right side). This is the last petrol station along the highway before reaching abu dhabi proper.

Keep in mind the petrol price in UAE is 3x compared to saudi.

I hope this helps. Have safe trip.