I just leased the new Volkswagen 2013 CC. Is it safe to use 87 octane gas even though it recommends 91 octane on the inside lid of the gas tank access?

it recommends it but it will run on 87, difference being there are alot more grades available, than the general public are aware, and the real performance cars will not run on 87, due to when the engine is designed to "detonate" in the cylinders, too high octane causes it to go early, and to low could be late, (you would feel vibrations), or hear the difference, but yes it is fine,

Low Octane gas will detonate before the ignition spark occurs causing a "ping" noise in a high compression cylinder. The proper fuel will not "detonate" if ignited by a properly timed spark ... It will burn at a known rate and reach peak pressure just as the piston is at or near Top Dead Center. Fuel that is detonated early in the cycle, will reach peak pressure before TDC causing the pinging noise causing power loss and eventually destroying your engine 91 octane is designed for such engines and will run fine in most gas engines - except any octane gas will ping if the engine is carbonized. The answer by John above is backwards.

Modern engine management systems such as found in VWs today will accommodate for lower octane fuel by altering engine operating parameters to reduce/eliminate ping. The downside is reduced performance and economy. You may find that running the 91 octane is actually cheaper than the 87 due to the improved fuel mileage.

I have a 2011 VW CC and I alternate using the lower gas octanes (can't even FIND 91), but I periodically add Octane Boost. So far I've not had any noticable issues. Opinions?