If it was a better eatery it could have been canola or (gasp) evoo
If it was your run of the mill place, I bet they get their salad dressing from SYSCO which would almost for sure be made with soybean oil.
@Rivvin...by now the toxins have hit your digestive tract...I think that you need to be evacuated (LOL)
"I am a member of PETA...People Eat Tasty Animals"
"Ah sir, we have a team of Inuit that goes and collects blubber from whales that die of natural causes. So, the oil in our vinaigrette is actually whale oil from whales that were not hunted by whalers."
"We use re-processed oil that we collect from McDonald's grease pits and then refine so we can re-use it for cooking and our salad dressings."