Design/methodology/approach In this study, the oil film strength of trimethylolpropane trioleate (TMPTO)-based lubricating oil was evaluated using a four-ball tribometer. To study the impact of multiple factors, the Taguchi L27 orthogonal array was used with four control factors at three levels. The Taguchi method provided an optimized parameter ranking based on the signal-to-noise ratio. In addition, the lubrication regime was characterized using the Stribeck curve. Findings The results indicate that the blend of sulfurized additives with TMPTO-based oil exhibited excellent oil film strength, owing to a synergistic effect that promotes the formation of a protective film layer on the surface. The temperature (44.09%) has the greatest impact on oil film strength, followed by oil type (23.78%), load (15.63%) and sliding speed (9.98%), as indicated by variance analysis. A desired friction coefficient for boundary lubrication ranges from 0.02 to 0.13, typically occurring at (ηV/p) = 0.5. Practical implications This work focused on a few parameters; however, comprehensive research incorporating operational conditions, material properties and structural variables across realistic surface roughness ranges could further refine the Stribeck curve for specific applications. Originality/value The analysis offers key insights into optimizing oil film strength and selecting suitable rheology for optimal lubrication in light of “Stribeck curve” for a specific regime of lubrication. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2025-0004/