I loaded a .wav file that was 3 megabytes into Audacity and exported
it back out as a .mp3 file. When I checked the results, I discovered
that the .mp3 file was four and a half megabytes in size!

As far as I know, .wav files are uncompressed whereas .mp3 files are
compressed. Therefore, if you convert a .wav file into an .mp3 file,
the result should be smaller (or at most, the same size) than the
original .wav file.

So why was this .mp3 file bigger? Was this just a fluke?