**1. Introduction**

Energy is a critical resource that all economies require to produce goods and services and to enhance human, social, and economic wellbeing [1–4]. It is needed by various industries as an input into the production of goods and services, for transportation, and by households for heating, cooking, lighting and powering domestic appliances. Empirical studies show that energy consumption is positively correlated with indices of economic growth and wellbeing [3]. This is why the provision of energy to most of the world's population has been identified as a criterion for assessing progress towards sustainable development. Both developed and developing countries, however, face a myriad of energy challenges that include inadequate and unsuitable supplies of energy sources, energy supply uncertainties, high and fluctuating prices of energy, and environmental pollution and degradation as a result of the production, distribution, and use of energy. For countries that rely heavily on energy imports from politically unstable regions, additional risks stem

from the threats of disruption to energy supplies and the destabilizing effects of such disruptions to their economies and energy markets [5, 6]. Examples of such disruption include the 1973 and 1979 oil crises, the disruption of world oil supplies during the Persian Gulf wars, and the disruption of natural gas supplies to Ukraine in 2014 due to disagreements with Russia [7]. More recently concerns have emerged from energy supply and storage infrastructure due to natural disasters and terrorism. For countries such as the United States, these challenges are intricately linked to their national security. For poor countries, these challenges have undermined their prospects of economic development and constrained their efforts to alleviate poverty and improve the standards of living of their peoples. They have also had an adverse impact on the balance of payments. Addressing these challenges has therefore increasingly become the centrepiece of the energy policies of many countries where the issue is being framed as one of enhancing energy security. This chapter examines energy security with a focus on its nature and meaning, its multiple dimensions, the indicators currently being used to measure energy security, and some policy measures that can be used to enhance energy security.

Grubb et al. [16] and Kruyt et al. [17], security of supply is a system's ability to provide a flow of energy to meet demand in an economy in a manner and price that does not disrupt the course of the economy. They further point out that non-secure energy systems are characterized by sharp energy price increases, reduction in quality, sudden supply interruptions, and long-term disruptions of supply. Sovacool [18–21], Sovacool and Brown [22], Sovacool and Mukherjee [23], Sovacool et al. [24], Brown and Sovacool [25], and Badea et al. [26] define energy security as equitably providing available, affordable, reliable, efficient, and environmentally benign energy services to end users. Brown et al. [27] opine that energy security has to do with questions of reliable energy supplies, regional concentration of energy resources, and the implications of strategic withholding of energy. They point out specific aspects of energy security such as electricity reliability, natural gas and petroleum security, and the vulnerability of the entire energy supply chain. They also maintain that robust global coordination of responses to energy supply shock is critical to energy security. According to APERC [28], energy security consists of

*Towards Energy Security for the Twenty-First Century DOI: http://dx.doi.org/10.5772/intechopen.90872*

4A's namely, availability, accessibility, acceptability, and affordability.

access to affordable, reliable, sustainable, and modern energy for all.

security, and provide energy security metrics for selected countries.

**3. Indicators of energy security**

**3.1 Energy reserves**

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Although the definitions of energy security provided above are not exhaustive, they all illustrate the importance of energy security, its multi-dimensional nature, and why many countries regard it as a policy priority. In the short-term, energy security concerns focus on the ability of the energy system to react promptly to sudden changes in the supply–demand balance. In the long-term, energy security concerns have to do with timely investments in energy supply in line with economic developments and environmental needs. At the multilateral and global levels, energy security has continued to receive increasing attention as evidenced by Sustainable Development Goal 7 of the United Nations that requires countries to ensure

Several indicators have been proposed for assessing the energy security risks that various countries face, how the energy security situations have been changing over time, and how energy security is impacted by the energy policies of these countries. Estimates of these indicators are valuable in developing energy security strategies that take into account countries' energy resource endowments, market conditions, vulnerabilities to energy supply shocks, and technological progress. In what follows I present some energy security indicators, explain their use in assessing energy

Energy reserves refer to the estimated quantity of energy sources (e.g. coal, gas, or oil) known to exist with reasonable certainty, and which can be recovered with presently available technology at an economically viable cost. A country's energy resources and the extent to which they are developed is an important determinant of energy security. In general, countries with vast energy resources are more energy secure compared to those with meagre energy resources. Over time, however, changes can occur that alter a country's energy resources and thus improve or worsen its energy security. For example, the discovery of vast oil and gas resources in the North Sea had a significant impact on Norway's economy and energy security and made Norway a rich oil-exporting country [29]. This is also the case with countries which have recently discovered new energy reserves. **Table 1** presents
