Also is their any sites on the net where you can purchase new or used owners manual,
Thanks in advance.

l have a gs 400 and l put regular in it all the time. its all the same. dont let them fool you.

Its all the same??? When you start having harsh shifting problems, lack of power and check engine lights remember
that its all the same. Lexus is are very sensitive to fuel quality.
Also the dealership is the best bet to getting the right owners manual for you vehicle. Hoped this helped.

l wouldnt use regular. it is high compression engine. it says premium gas only, the car company wont ask you to put premium for no reason. come on if u have a gs, which is a sweet car, dont feed it junk!.

Look at the fuel gauge. Most cars that need premium will have it printed on the gauge itself. l have a 1990 and a 1996 Caddy and both have it printed right on the gauge.

You can this site for free down-loadable owners manuals:
http://analogstereo.com/lexus_gs_owners_manual.htm

You can check the owners manual for the fuel & maintenance ''Requirements''...

do not buy a luxury car if you can not afford premium fuel.

Suggest that you run premium in that car. You can run mid grade gas in it. Just remember that the lower the grade of fuel that you run the less performance you will have, the more spark knock the engine will make, and it will also increase carbon build up in the engine. More carbon means a engine that will produce less power over time.