My cavalier?  It looks like GM Parts Direct discontinued a few locking gas caps they once were selling.  I went through one aftermarket cap, which failed, and I am on my second aftermarket cap.  This locking cap is ok, but nowhere near as good as the cap I bought from GM a few years ago for my other car.
Any help would be appreciated.
 
by aftermarket, you mean one you got at like autozone or kragen or something? 
i got one a few weeks ago and my mileage has dropped a little bit. i wonder if i got a bad cap...
 GO PATS!!!
GO PATS!!!
 
Yup from autozone.  I just want a good cap that I won't have to replace every 6 months or a year.  GM sometimes used to make good parts.