A321 pilot reported a decreasing oil quantity during cruise from one of two previously reported high oil consumption engines. The crew diverted and landed safely at an alternate airport before an engine shutdown was required.

Narrative

On Day 0 we were operating Aircraft X from ZZZ2 to ZZZ1. Both engines are on a HOC (high oil consumption) watch. The required 'every flight' reinspect was accomplished prior to leaving ZZZ2. Both engines were indicating about 20 quarts of oil at ZZZ2. As the flight continued we noticed the number 2 engine having slightly less oil quantity than the number 1 engine. About halfway through the flight we noticed the number 2 engine indicating around 11 quarts of oil. Then about an hour and forty-five minutes (1:45) from ZZZ1; the number 2 engine was indicating 7 quarts of oil. At all times the oil pressure and temperature remained normal.At this time I initiated a satcom call to Dispatch and Maintenance Control. As we were discussing the issue for about 15 minutes; the quantity indicating fell to 5 quarts and we received a blinking ECAM advisory. All of us agreed to do a precautionary diversion to ZZZ to avoid having to shut the engine down if we continued to ZZZ1.On final approach to ZZZ the number 2 engine oil quantity got down to as low as 3.0 quarts indicating. Oil pressure and temperature still remained normal. The quantity fluctuated between 3-4 quarts as we taxied to the gate. Upon engine shutdown the quantity indicated 8.5 quarts. I made an entry into the aircraft logbook with the details described concerning the possible oil leak in the engine.After our business partner Maintenance Control inspected the engine; they informed us that they found signs of an oil leak; most likely at the oil/fuel heat exchanger. At this point Maintenance Control took the aircraft out of service.