During poultry processing, gas stunning systems are based on the birds exposure to gases which may induce either anesthesia or anoxia. Research comparing electrical and gas stunning have reported differences in incidence of carcass defects and variation in meat quality traits. However, contradictory results have been reported, especially when different stunning conditions were compared. Three trials were conducted to evaluate breast meat quality of broiler chickens (2.5 kg live wt.) processed using electrical (E) (constant voltage of 120V pulsating DC, 200 Hz, 4.6 s; 60 mA/bird) or gas (G) stunning with carbon dioxide exposure (5.5 min). Birds that were gas stunned remained in crates that were passed through underground chamber with gas concentrations increasing from 10 to 32% (Linco® system). After slaughter and chilling, the incidence of carcasses with blood-engorged wing veins and/or blood spots on breast meat was evaluated (n = 144/stunning system). Breast (P. major) muscles were deboned immediately after air chilling (commercial deboning time, 2.5 h) or after 6 and 24 h postmortem (n = 36/deboning time/stunning system; n = 216). The meat pH was determined immediately after deboning, whereas color (L*a*b*), cook yield, and AK-shear of cooked meat were determined after 24 h postmortem. In comparison with electrical stunning, gas stunning produced a noticeably lower incidence of carcasses with blood-engorged wing veins and/or blood spots on breast meat (18.7 vs. 61.8%; P < 0.01). The stunning system did not influence breast meat postmortem pH fall, color, and cook yield. Gas stunning resulted in a lower AK-shear values when fillets were deboned after 2.5 h of aging (4.86 vs. 6.89 kg/g; P < 0.01); however, shear values were similar for both treatments when fillets were aged for 6 or 24 h postmortem. Using the conditions adopted in the present study, the major advantages of gas stunning over electrical stunning are the lower incidence of breast meat defects and lower AK-shear values of cooked meat for fillets deboned immediately after chilling .