In this study, we perform an efficiency analysis of Canadian oil and gas firms. Using data envelopment analysis, technical, managerial and scale scores from ten samples built from 110 oil and gas companies, listed in Canadian stock exchanges, are computed for the years 2012, 2013, 2014, and 2015. Our analysis, supported by appropriate statistical tests, confirms that the Canadian oil and gas industry exhibited predominantly low overall technical efficiency levels both for each of the years and overall for the four years. We have observed that the main source of inefficiencies was the management of operations. In addition, we have seen consistently that across the samples, a statistically significant relationship exists between the efficiency scores and the size of the companies. Finally, we have observed the existence of a relationship between the efficiency scores and the type of producer (pure oil vs. oil and gas), but we could not reach conclusions on the best performer that was consistent across the samples.