The identification and validation of humane methods to euthanize piglets is critical to address public concern that current methods are not optimal. The blunt force trauma procedure is humane when carried out correctly, but most people find it aesthetically objectionable. The use of carbon dioxide is often recommended, at the same time it is criticized as being aversive to swine. This research sought to: 1) evaluate the aversiveness of inhaling nitrous oxide and oxygen, using our previously validated approach which relies on the piglet’s perspective, and 2) validate the effectiveness and humaneness of nitrous oxide to induce loss of consciousness by electroencephalogram (EEG) recording. Three experiments were conducted to determine the aversiveness and the effectiveness of different mixtures of gas to euthanize piglets. The gas mixtures tested were nitrous oxide (“laughing gas”) and air (90%:10%; ‘90N’); nitrous oxide, oxygen and air (60%:30%:10%; ‘60N’); and carbon dioxide and air (90%:10%; ‘90C’). Experiment 1.a. allowed piglets to walk freely between one chamber filled with air and another chamber prefilled with either 60N or 90N. Experiment 1.b. performed the same test except the gas chamber held nitrous oxide prefilled at 25%, 50%, or 75% concentration in air or carbon dioxide prefilled at 7%, 14%, or 21% concentration in air. Experiments 1.a. and 1.b. showed that piglets do not find exposure to nitrous oxide aversive, but at high concentrations hypoxic conditions (lack of oxygen) caused the piglets to breathe heavily. Carbon dioxide more often resulted in flailing behavior at 21% prefill whereas Nitrous oxide at 75% prefill caused 2 out of 7 piglets to flail but 4 out of 7 became sedated. Experiment 2 measured brain activity through EEG to assess loss of consciousness as they pigs were subjected to 60N, 90N or 90C. The EEG results backed up the behavioral studies by demonstrating that there are differences between the 3 treatments in terms of effects on the brain. This means that the behavioral changes seen reflect differences in the animal’s perceptive experience of the treatments rather than, for example, alterations in motor function. In that sense, the EEG data strengthen the link between the behavioral results and the implications for animal welfare that nitrous oxide is less aversive than carbon dioxide, although taking slightly longer to take effect; 71 vs. 59 sec in experimental settings. Furthermore, this project demonstrated that 90% nitrous oxide in air can kill piglets.