This is a Gravina Crime Family mission.
"Sal Gravina runs smuggled gas across the country in tankers. Each tanker is worth thousands of dollars to him. It would be a great shame if his trucks got destroyed somehow. Gas is so flammable after all... Destroy the tankers."
This is a rather fun mission where you get to blow up five tanker trucks. When you begin, drive towards the moving marker on your mini-map. Once you reach it drive a short distance ahead and stop, then get out of your car and ready a weapon. You'll want to shoot the tanker a fair distance from both you and your vehicle as it puts off a rather large explosion when it goes and can easily take you or your car with it.
Once you're done with the first, get back in your car and drive to the Trago gas station in West Side where you will find the next two tankers parked and guarded by up to four gangsters. Park across the street where you have a good line of sight on both trucks and shoot them. Afterwards you can take out any gangsters that survived the blast or just hop in your car and head to the last two that are parked at the gas station in East Side. Repeat the process here then drive the rather long distance to the safe zone in Midtown to end the mission.
- If you want to avoid police involvement on this one just look at your mini-map and wait for any police cars to leave the area before you blow the tankers. The mission gives you ample time to complete and the few seconds you wait will be quicker than dealing with the cops.