All things being equal, higher displacement engines will consume more fuel.

But all things ARE NOT equal. Engine size is just one part of the equation. There are tons of other things like gearing, transmission type, aerodynamics, vehicle weight, technology (e.g. cylinder deactivation), etc.

Just basing it on displacement alone is like saying a 2.5 engine is more powerful than a 2.0 engine. It just aint true...