I have had this happened to me twice now. while in flight I get a "using reserve fuel" message from the CDU yet both wing tanks are about 90 % full.any thoughts are appreciated.R. Gumler

That means that the remaining fuel at the end of the flight will be less than the amount you set on Reserve fuel on the Init Page.That message will not appear if the estimated fuel at destination on the PROG page is greater than the reserve fuel on the init page.Hope i made my self clear, English it's not my first language

Also note that entering "5" equals 5,000 lbs.So if you are getting the message at 90%, you are probably entering "41.5" or higher being 41,490 lbs is 90% capacity of the default engines in the PMDG 738A good rule of thumb is to set up your flight plan and check the PROG page for fuel remaining at landing runway. Make sure it is no less than 5k lbs. I like this to be closer to 7-10k and enter "5" in reserves this way I don't get the message if I'm say 4,900 lbs at touchdown.

Thank you very much Matias!!! yes, that makes sense.

Thank you also Cory, will do. I did in fact landed with < 5k good stuff. Collective knowledge is what the forums should be about.