Recent research has demonstrated a reduction in dietary heat increment and improvements in production performance from supplementing lipids as an energy source. This performance improvement can be attributed to increased availability of nutrients from feed ingredients, in addition to improved energy efficiency by increasing net energy (NE) of diet. The present study was conducted to evaluate the effects of increasing metabolizable energy (ME) levels in the diet on performance parameters, nutrient digestibility and energy balance of 19 to 41 d of age broilers kept in thermoneutral conditions. A total of 336 male broiler chickens were evaluated in this study, distributed in a completely randomized design with 4 treatments and 6 replicates with 14 broilers each. The treatments consisted of 4 diets containing 19% CP and increasing ME levels (2,980, 3,080, 3,180 and 3,280 kcal/kg), which were obtained by addition of soybean oil. The data were submitted to ANOVA and the means were compared by the Tukey test (α = 0.05). Feed intake was not affected by ME levels; although the best results for weight gain (2.3 kg) and feed conversion ratio (1.53 kg/kg) were obtained in broilers fed with diets containing 3,280 kcal/kg (P < 0.01). The viability rate and feed cost per kg of live weight did not differ between treatments, but production efficiency ratio increased linearly as ME was increased (P < 0.01). The ME levels affected the EE digestibility, broilers fed with more energetic diets (3,180 and 3,280 kcal/kg) achieved better EE digestibility (79.8% and 81.4%, respectively; P < 0.01). Heat production and increment was not affected by ME levels. The dietary ME levels had a linear effect over NE (P < 0.03), but ME conversion into NE remained constant between diets. In conclusion, ME levels has influence on performance and energetic metabolism of broiler chickens under thermoneutral condition.