B757 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Type 1188
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed in Emergency Condition
Aircraft
In cruise at 29;000 ft; the Captain noticed that the left engine oil quantity was at 0. He brought the issue to my attention and we both noticed that the oil pressure indication had dropped and was erratically hovering around 20 to 27. We ran the 'Engine Oil Press' checklist which prompted the 'Engine Shutdown Checklists.' After contacting Dispatch; we decided to divert. We notified the Flight Attendants and passengers. While receiving guidance from ATC; we completed the appropriate checklists and landed safely as per SOP. Upon inspection by Maintenance personnel; it was determined that the engine was completely out of oil.
The left engine oil quantity indicated zero; and the left oil pressure was slowly decreasing yet still in the normal range. We ran the oil pressure QRH. Since the oil pressure was continuing to fall we also reviewed the Engine Shutdown checklist. The oil pressure dropped into the caution range and [the engine] was shutdown using the QRH.
B757 flight crew reported loss of left engine oil quantity in cruise.  The crew elected to shut down the engine and divert.