EMB-145LR flight crew reported engine oil leak in cruise flight. Performed engine shutdown and diversion for uneventful landing.

Narrative

I completed a walk around in ZZZ and saw no visible oil leakage on either engine. We departed ZZZ runway XXR with 9 quarts of oil. I was pilot flying and my captain was pilot monitoring. Once reaching our cruise altitude of FL310 we ran the cruise checklist; it was at this time the oil capacity read 2 quarts. My captain brought this to my attention and we discussed the possibility of a wrong indication and next steps; we decided to monitor indications but for now would operate as normal operation with priority handling. My captain at this point requested priority handling without an emergency due to low oil quantity into ZZZ1. We were given a descend via clearance on the ZZZZZ. At FL300; I turned on APU with special attention since a generator was MELed and we had previously briefed to turn it on if precautionary if we lost an engine. He requested QRH and reviewed the engine out procedure; we discussed runway availability; and that I would continue flying if comfortable. I believe at this time my captain called into the back to talk to flight attendant; and I took radio one. I noticed during that time the oil pressure indication was slowly falling; about 10 psi every minute. I alerted my captain and we prepared for engine shutdown. At 33 PSI; low oil pressure EICAS message became illuminated and we completed that check list. It led us to the engine shutdown checklist; my captain read and I verified. I brought thrust lever to idle; he completed subsequent items. He checked runway length and determined the safer option would be to divert to ZZZ2. He handled radio communications from this point on and my primary objective was to fly the airplane. I know he [requested priority handling]and requested ILS 25L; they gave us vectors all the way in. He advised our FA of our situation and once the aircraft was secured and checklists completed; he advised passengers. I suggested we let the passengers know we are having a maintenance issue and needed to divert to ZZZ2; but avoid using word emergency or engine failure. I remember ATC asked what distance we wanted to be brought in at and we came in at 10 miles. We flew it in green needles from the point of diversion and handled all checklists appropriately. My captain asked if I were confident in my ability to fly and I chose to continue. He asked for me to disconnect autopilot at 1000' and at 500' he took the aircraft to landing without any further incident. We exited [taxiway] 1 of our own power. No assistance on the ground was needed and we taxied back to the FBO. Upon inspection of the left engine; there was visible streaking and oil leaking and pooling under the left engine. We put a bucket under and cardboard under engine when parked.Cause: Low oil pressure due to low oil quantity; oil leak.Suggestions: There was nothing we could've done to prevent this event from occurring; it was handled exactly as we trained for it. Reiterating the importance of training how you plan to execute and taking the training seriously. The captain showed complete professionalism and leadership; I am happy to fly alongside him any day.