l found a stain with oil on my volvo s80 is driver side floor. l have no idea what it might be. l smelled it and i'm pretty sure it is oil. Does anone have an idea what that might be?

You just answered your own Q

Could well be brake fluid.

Put your hand up as high as you can on the pedal lever, if it comes off oily get it sorted.

Do not be tempted to ignore it.

Weird. can not think what would be causing that. Sorry if this sounds retarded but did you have oil on your shoes? Try taking the carpet up and see if that gives you any clues.

Also the S80 is a sweeet car.

Check your fluids., i.e. brake fluids as said above, even power steering fluid.

What color is the fluid? Is it possible it is engine coolant?

If it is green,
its coolant.
And that means you have a bad heater core.