Narrative:

We taxied out to runway xxl in ZZZ without any incident. Takeoff was normal with normal indications. We weighed 170;000 pounds and had almost full tanks of gas with a full load of passengers heading to ZZZ1. Shortly after takeoff the captain asked if I smelled anything. I replied; 'yes.' it was not the normal galley/food smell; high heat smell or electrical burning smell; but more of a burning oil smell. I associated it with the possible factories that we fly over in the ZZZ area. The captain called the flight attendants to see if they smelled it and they also smelled it in the back of the cabin. Once the captain heard this; he said that we were going to return to ZZZ. I put my mask on and established communication (comm) and the captain did as well. ATC asked if we were declaring an emergency and the captain responded; 'yes.' the captain ran the checklist and I put the autopilot on and began the decent back to ZZZ for a landing on xxl. We were only about 20 miles from the airport when we began the return. My thought process was to get the aircraft on the ground as soon as possible and the captain seemed to be the same. He ran as quickly as possible through the smoke/odor/fumes checklist while I set up for a 40-flap max brakes; overweight landing. We came back together on final and ran through the approach/descent; approach checklist and set up to land. After landing we called the flight attendants to see if they saw or smelled any more odors. They did not and we proceeded to the gate. Maintenance met us at the gate and said that they had borescoped the engine the night prior. They said that nine out of ten times that is the cause of the smell.

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Original NASA ASRS Text

Title: A Captain and First Officer report about a burning oil smell in the flight deck and cabin of a NexGen B737 aircraft shortly after takeoff. An emergency was declared and an air turnback accomplished. Maintenance noted that a Borescope Inspection had been accomplished on the CFM-56 engines the night before.

Narrative: We taxied out to Runway XXL in ZZZ without any incident. Takeoff was normal with normal indications. We weighed 170;000 LBS and had almost full tanks of gas with a full load of passengers heading to ZZZ1. Shortly after takeoff the Captain asked if I smelled anything. I replied; 'Yes.' It was not the normal galley/food smell; high heat smell or electrical burning smell; but more of a burning oil smell. I associated it with the possible factories that we fly over in the ZZZ area. The Captain called the flight attendants to see if they smelled it and they also smelled it in the back of the cabin. Once the Captain heard this; he said that we were going to return to ZZZ. I put my mask on and established communication (comm) and the Captain did as well. ATC asked if we were declaring an emergency and the Captain responded; 'Yes.' The Captain ran the checklist and I put the autopilot on and began the decent back to ZZZ for a landing on XXL. We were only about 20 miles from the airport when we began the return. My thought process was to get the aircraft on the ground as soon as possible and the Captain seemed to be the same. He ran as quickly as possible through the Smoke/Odor/Fumes Checklist while I set up for a 40-Flap max brakes; overweight landing. We came back together on Final and ran through the Approach/Descent; Approach Checklist and set up to land. After landing we called the flight attendants to see if they saw or smelled any more odors. They did not and we proceeded to the gate. Maintenance met us at the gate and said that they had borescoped the engine the night prior. They said that nine out of ten times that is the cause of the smell.

Data retrieved from NASA's ASRS site as of July 2013 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.