Burns oil on long journeys

Hi all, 

I've had my 53 plate VW Polo 1.2 for a couple of months now. 

Very occasionally I do a hour and a half drive and all of my oil disappears  - I suspect my car is burning it, but it only does this after I've done this drive. 

When I got there it was almost empty, so after I filled it up and came home, it was empty again. In total I've topped it up 3 litres. 

A friend told me it could be my piston rings but I'm unsure as to what it could be. 

Thanks.