**5. Conclusions**

The physico-chemical characterizations of the biodiesel, i.e., flash point, pour point, cloud point, and density, have been found within the ASTM (D6751) and (EN14214) standards. The values of fuel properties were comparable with mineral diesel. FT*-*IR, NMR, and GC–MS analysis established the total conversion of crude oil to FAMEs. The elemental analysis of biodiesel ensured the feasibility for environment friendly usage. These sources have been optimized through optimization of transesterification reactions: oil to methanol ratio (6:1), a potassium hydroxide concentration (3.0%), temperature (65°C), stirring rate (700 rpm) and reaction time (60–80 min). The highest biodiesel yield was obtained from *Albizzia julibrissin* (98%) followed by *Acacia farnesiana* (96%), *Koelreuteria paniculata* (95.2%) and *Koelreuteria paniculata* (93.33%). FAMEs of all sources were compatible to ASTM (D6751) and (EN14214) standards. These non-edible plant seeds offer a cheap source of renewable energy. These plants can be easily grown on barren and wastelands and contribute to efficient biodiesel production to curtail the energy crisis. Keeping these findings in preview, we can assert that biodiesel obtained from these non-edible seeds has a huge potential as an alternative to petroleum diesel and can be efficient renewable source of fuel.
