It depends.
Person 1: "She said to meet us at the gas station."
Person 2: "No, she said to meet us at the petrol station."
Person 3 "..."
Person 1: "It's synonymous, dipsh!t."
Person 2: "It doesn't matter. You were wrong about what she said! Liar!"
Person 3: "..."
Person 1: "The exact words are what do not matter. Petrol and gas are synonyms."
Person 2: "Nuh uh! Gas doesn't always mean gasoline and petrol is just short for petroleum, which could just as easily mean crude oil or any other stage of petroleum refinement.
Person 3 "..."
Person 1: "Context matters. They are synonymous in the context of refueling stations, Mr. Know-it-all. I'm sure she didn't want us to meet her at the helium factory or the oil refinery."
Person 3: "Guys! Guys! Guys! STFU already! We're here now. Jesus. *exhale* Frickin' idiots."