1999 Mercury Grand Marquis - which gas

what gas is a nono for a 99 merc ls or can I use all gas that is top tier has ethanol ?

A 99 should be fine with the “contains upto 10% ethanol” gas. Not designed for higher ethanol gas.


Agree w @Purebred. Just stay away from E85


I’ve seen E15 around here lately. What about that?

Not on a 1999, I wouldn’t! Old fuel lines, old rubber seals, old pump impeller… they just don’t need that stress.


If you still have your owners manual, see what fuel it recommends.

It wants regular. I agree no more than 10% ethanol.

Doesn’t the Costco gas contain up to 10% ethanol, according to the labeling at the filling station . . . ?

If op is a member, I’d just get gas there

Along with any other brand of gas, pumps are clearly labeled.