The Danish energy supply was well-functioning before the oil crisis began in 1973, but the country was highly dependent on imported oil. Thus, the crisis hit a key nerve in its society. This paper analyzes the energy supply before and after 1973, especially the immediate and long-term measures taken to ensure supply security. I argue that the two most important features were the establishment of a regulative regime and the construction of a diversified energy supply. Governmental regulation was considered a precondition for a successful turnaround of the energy sector from an extreme dependency on imported oil to a diversified energy mix. However, increased CO2 emissions soon made evident that the multi-tier energy supply system was fairly short sighted, and, in the wake of the Brundtland Report, Denmark entered a new and more climate-friendly path.