A study of exhaust emissions from engines in Enugu State, Nigeria fuelled with petrol, diesel and their blends with biodiesel was carried out. The biodiesel was produced from waste cooking oil via transesterification and both were analysed using ASTM methods. Exhaust emissions (CO, CO₂, O₂, NO and NOx) from petrol (motorcycles, tricycles, mini-buses and passenger cars) and diesel vehicles (tankers and trailers) as well as big and small capacity generators were analysed using a Bacharach portable combustion analyzer 2. Petrol and diesel were blended with biodiesel and used to fuel generators and vehicles at different blend ratios (B5 to B40). The diesel vehicles emitted much lower concentrations of CO and CO₂ but higher NOx than the petrol vehicles. Small capacity generators emitted more CO while large capacity generators emitted more NOx and CO₂. For all blends, there was a significant reduction in CO, CO₂ and NOx emitted in the small and large petrol-biodiesel generators. However in the diesel-biodiesel generator there was an increase in NOx emission and a decrease in CO and CO₂. Also, CO from all the petrol vehicles exceeded the obsolete EU 2 limit. Therefore, these emissions could enhance health and environmental hazards associated with their pollution.