Guide on how to refill your gas stations.
First of all you need a trailer and a oil tanker which looks like the photo given below.
Then you should move to one of the refineries whose locations and screens are given below
The first refinery which is located at flint county, It's near LS-SF tunnel.
The 2nd refinery which is located at bone county, It's at the oil pumping job which can be found in /gps.
After reaching at one of the refineries you must type the command /refilltrailer and the tanker will start filling it can be filled maximum with 1000 Units which cost 10$ per unit and after filling the tanker you should go to the gas station you wanna fill and type the command /refillreservoir and It'll fill the pumps of gas station, maximum of 5000 units can be filled in pumps.
Note: If there are more refineries then tell me and I'll update this topic,