1999 Chevrolet Cavalier

Brakes problem
1999 Chevy Cavalier 4 cyl Front Wheel Drive Automatic 134065 miles

My brakes went write down to the floor. The brake fluid is fuel. There is no leak. What could it be? I don't want to start changing the calipars and lines or drums if it isn't that. The pads are fine. How couold I tell if the calipars are not working?
July 1, 2010.

Master cylinder probably failed. It can have an internal leak where the fluid level would remain the same but the fluid isn't actually getting to the brakes, it's just leaking from one spot to the other in the master cylinder.