Does one-engine cruise consume less fuel than two-engine cruise?
For an A320, at FL 100 and weight 50 tonnes and ISA, the FF is 1028 kg/h per engine, so two engines is 2056 kg/h.

Now for the same but OEI: the FF is 1891 kg/h (just the one engine).



Scenario 1 is higher fuel flow rate. I'll explain why based on scenario 2.

In scenario 2, with one engine inoperative (OEI), the remaining engine will run at higher power setting, which improves the SFC (see image below), and therefore will improve the endurance (time in the air; how fast the fuel is used).

► It will diminish the range though, as range requires speed, which will be limited with OEI (and also due to the low altitude), i.e., don't mix the improved FF and endurance with why not always fly with one engine (ignoring the safety issues).


Source: Jet Transport Performance Methods, Boeing

(Don't miss the text left of the graph.) That's also why coast guard C-130s orbit with an engine deliberately turned off. Being a turboprop (gas turbine), the SFC relation holds.



Related: Why is max endurance different for jet and props?