This research focuses on drawing a comparison between how the UK and Brazil have managed their energy mixes since the oil crisis of the 1970s to the present time. The analysis is based on four variables: diversification, power, sustainability and efficiency. The main hypothesis assumes that the evolution of energy mixes is more related to the available natural resources and the physical features of both countries than to political decisions. Technically, we used official data organized into graphs and charts for the decades of 1970, 1980, 1990, 2000, 2010 and 2017. The preliminary results showed that in both countries, all the variables changed positively, but the efficiency has been higher in the UK since the British GDP increases with the increasingly drop in energy production. Therefore, these preliminary results showed that the hypothesis better explained the Brazilian context than the British context.