Ireland imports 88% of its energy requirements. Oil makes up 59% of total final energy consumption (TFC). Import dependency, low fuel diversity and volatile prices leave Ireland vulnerable in terms of energy security. This work models energy security scenarios for Ireland using long term macroeconomic forecasts to 2050, with oil production and price scenarios from the International Monetary Fund, within the Irish TIMES energy systems model. The analysis focuses on developing a least cost optimum energy system for Ireland under scenarios of constrained oil supply (0.8% annual import growth, and 2% annual import decline) and subsequent sustained long term price shocks to oil and gas imports. The results point to gas becoming the dominant fuel source for Ireland, at 54% total final energy consumption in 2020, supplanting oil from reference projections of 57% to 10.8% TFC. In 2012, the cost of net oil imports stood at (sic)3.6 billion (2.26% GDP). The modelled high oil and gas price scenarios show an additional annual cost in comparison to a reference of between (sic)2.9bn and (sic)7.5bn by 2020 (1.9-4.9% of GDP) to choose to develop a least cost energy system. Investment and ramifications for energy security are discussed. (C) 2013 Elsevier Ltd. All rights reserved.