A B737-800 lost right engine oil quantity and pressure at cruise because the engine was incorrectly install prior to this flight. An emergency was declared and the flight diverted.

Narrative

In cruise the First Officer called out a loss of oil pressure on number 1 engine. Oil pressure was in the red at 8 PSI and remained at that reading to landing. Number 1 throttle was reduced to idle immediately and thereafter oil quantity went to zero. LOSS OF OIL PRESSURE Checklist led to ENGINE FAILURE or SHUTDOWN Checklist and the engine was secured. The First Officer was designated to land the aircraft. I called ATC and declared an emergency requesting a lower altitude and declaring a nearby airport for diversion. I completed all remaining checklists; notified flight attendants; passengers; and Dispatch and then landed uneventfully. I have no suggestions for avoiding a recurrence as the problem was caused by a maintenance issue. However; I can offer the following; the aircraft assigned to us had just had an engine replaced and this was the first flight after engine change. I was concerned so I left the lower Display Unit on during flight to monitor engine parameters. At top of climb; the left side showed seventeen quarts of oil and the right side showed eighteen quarts of oil. I saw no abnormal indications until the loss of oil pressure was discovered in cruise.