Narrative:

Engine oil service cap left off of right engine causing loss of all but 1 gallon of oil and aircraft air return to ZZZ. Climbing through 700 ft after departing runway; ATC noted a dark exhaust from our #2 engine. We switched to departure and felt nothing unusual with the airplane. After we cleaned up the aircraft; we noted that the #2 engine oil quantity was 1 gallon. We reduced thrust to idle on that engine and requested return to ZZZ. We declared an emergency. We did the 1-ENG inoperative checklist and landed. Crash fire rescue equipment followed us to the gate.

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Original NASA ASRS Text

Title: ADVISED OF SMOKE TRAIL BY ATC; B737-200 RETURNS TO DEP ARPT WHEN R ENGINE OIL QUANTITY DROPS DUE TO THE OIL CAP NOT IN PLACE.

Narrative: ENG OIL SVC CAP LEFT OFF OF R ENG CAUSING LOSS OF ALL BUT 1 GALLON OF OIL AND ACFT AIR RETURN TO ZZZ. CLBING THROUGH 700 FT AFTER DEPARTING RWY; ATC NOTED A DARK EXHAUST FROM OUR #2 ENG. WE SWITCHED TO DEP AND FELT NOTHING UNUSUAL WITH THE AIRPLANE. AFTER WE CLEANED UP THE ACFT; WE NOTED THAT THE #2 ENG OIL QUANTITY WAS 1 GALLON. WE REDUCED THRUST TO IDLE ON THAT ENG AND REQUESTED RETURN TO ZZZ. WE DECLARED AN EMER. WE DID THE 1-ENG INOP CHKLIST AND LANDED. CFR FOLLOWED US TO THE GATE.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.