Tribological behaviour of biodiesel should be investigated to get confidence for long-term engine usage. Also, the higher nitrous oxide (NOx) level from the biodiesel-fueled engine is observed. Tribological assessment and engine performance of lower blends of palm biodiesel (B10, B20) are available in the literature. Due to limited reserves of fossil fuels, the demand for biodiesel is increasing day by day. To fulfil this demand, the higher blends of biodiesel (such as B80, B90) should be investigated. Hence, this study aimed to investigate the tribological and NOx assessment of the higher blends of palm biodiesel. Palm biodiesel was produced by transesterification and blended with oleic acid (OA) and ethanol (E). Biodiesel blends such as 100% biodiesel (B100), 80% biodiesel + 20% oleic acid (B80OA20), 90% (80% biodiesel + 20% oleic acid) + 10% ethanol (B80OA20E10), 90% biodiesel+10% oleic acid (B90OA10), and 95% (90% biodiesel + 10% oleic acid) + 5% ethanol (B90OA10E5) were prepared. Pin on disc machine was used for tribological study and diesel engine was used for NOx analysis. Nearly 40% reduction in wear and 48% reduction in friction were observed for B80OA20 compared to B90OA10, while B90OA10E5 exhibited the lowest frictional force among all the test fuels. During tribological assessment, two blends B80OA20 and B80OA20E10 showed satisfactory performance and were further studied for NOx analysis. Also, these two blends lower NOx emissions by 12% and 2%, respectively, compared to B100.