Abstract The objective of this paper is to report our results on the behavior of an Otto engine working with gasoline blended with a fraction rich in esters of carboxylic acids derived from biomass pyrolysis bio-oil, hereby called as “Bioflex”. Sugarcane trash undergoes a fast pyrolysis process at the PPR-200 pilot plant to produce the bio-oil at Unicamp (Brazil). The process of separating carboxylic acids from bio-oil, the production of esters from these acids, the process of blending these esters with gasoline as well as the results of the use of this blend in an Otto engine of 4 kW capacity – component of a 2 kW e generator – are described. Trial tests determined that it is possible to blend up to 14 vol.% of Bioflex with gasoline type C used in Brazil. The engine performance with this blend compared to the performance of the engine working with pure gasoline resulted in identical power output and fuel consumption. The results showed that it is technically feasible to use blends of carboxylic acid esters derived from the biomass pyrolysis bio-oil with gasoline in conventional Otto engines.