Our 2006 XJ8 calls for premium gas, however due to hurricane Harvey most of the stations in town are out of premium. What are the alternatives?
I know that a little regular unleaded shouldn't damage the car but performance will lag. Is it possible to run it on regular with an over-the-counter octane booster?

 

We regularly run regular unleaded in both of our 4.2's with no ill effects. Granted I drive like a grandpa most of the time...I wouldn't recommend taking it to the track with that in the tank.

 

You can try getting octane booster

 

I've been tracking this subject for the 10 years I've owned a Jag with the 4.2 engine. There's no evidence whatsoever that use of of regular octane (87AKI) fuel will do any damage even on a long term basis. Many users see no reduction in performance or mileage.

Don't waste money on octane boosters, They're either snake oil or make an insignificant change- ie. raises the rating from 87 to 87.1 per bottle per tank.

 

Put in 89 for the interim.

 

f they don't have 91 they won't have 89. The pumps blend it half 87 and half 91 just before it enters the hose.