C152 pilot reported engine failure during cruise. Pilot made a safe off-airport landing with no damage or injury reported.

Narrative

While en route from ZZZ to ZZZ1 with one passenger on board; approximately 30 minutes after departure; I began to notice intermittent engine vibrations that initially seemed minor. As the vibrations persisted; I referred to the engine roughness checklist and followed the recommended procedures. However; the roughness did not improve right away. After a short period; the vibrations seemed to subside; but the issue resurfaced with much greater intensity. The engine vibrations worsened significantly; and the RPM began to decrease. Despite adding full throttle; the engine was only producing 1500 RPM; and the RPM continued to drop gradually. Initially; I considered diverting to the nearest airport; ZZZ2; a small regional field; but as the RPM continued to decline and I began losing altitude; I decided it was safer to stay close to the field below me; fearing the engine might fail completely before I could reach the airport.The roughness became so severe that I felt that the screws will almost come off the engine cowling due to the extreme shaking. At this point; I realized the situation was more critical than just engine roughness. Soon after; I noticed smoke starting to enter the cabin; which confirmed my growing suspicion that I was experiencing a complete engine failure.After that; I lost all my power from the engine. I squawked XXXX and made a radio call on 121.5 MHz to notify ATC of my [situation] and intent to perform a forced landing. I then selected an open farming field below as the landing site.The forced landing was uneventful; and my passenger and I were uninjured. The aircraft landed safely without flipping or sustaining any damage. After landing; I observed oil on the ground beneath the aircraft; which led me to believe the engine failure might have been caused by a loss of oil.After landing; I immediately contacted the appropriate persons.the passenger and I were unharmed; and the aircraft sustained no damage. The forced landing was successful; and there were no further complications. The presence of oil on the ground after landing confirmed the suspicion of oil loss as the likely cause of the engine failure.