B757 Captain is informed of smoke in the cabin passing FL200 in the climb. While working the problem the right engine oil quantity is noted at zero. The crew declares an emergency and returns to the departure airport for an over weight landing with both engines operating.

Narrative

At approximately 15 minutes into the flight climbing through FL200 I received a call from the flight attendants in the mid cabin that a strong odor was present. The smoke alarm in the mid galley went off almost immediately followed by the smoke alarms in the aft lavatories. Requested level off at FL260 to work the problem. Smoke was now reported in the cabin. A clearance to return to departure airport was requested and received from Center. The right recirculation fan was turned off. It was now noted that the oil quantity in the right engine was at zero. All other indications were normal. At this point an emergency was declared with Center and expedited handling was received to ZZZ. On the arrival the right engine low pressure light illuminated. It was now suspected the right engine was the source of the cabin smoke and the right aircraft pack was turned off. The smoke was reported to be dissipating. Experiencing occasional moderate turbulence and a strong gusty crosswind and an upcoming overweight landing at 225;000 LBS it was deemed safer to continue and approach with the right engine running until touchdown. The right engine was then shut down. The aircraft was inspected by ARFF. No further incident.