As a response to the Russian dominance of the EU's natural gas supplies and the EU's increasing gas demands, major gas pipeline projects are currently under way to enhance the EU's energy supply security. Oftentimes to raise financing and to allocate gas transportation capacities, auctions are carried out to allow gas shippers to book transportation rights. In recent years, auctions have emerged as one of the most successful allocation mechanisms in the microeconomic theory. However, different auction designs can lead to different outcomes making the choice of auction design a decisive one, especially for divisible-good auctions. This paper seeks to give a formulation of an optimal auction design for gas pipeline transportation capacity. Specifically three different mechanisms are tested: (i) NPV allocation; (ii) pro rata allocation; and (iii) optimization. In addition, Nabucco is taken as a case study to empirically show results of such auction designs. Results show that a trade-off between revenue optimization and fair allocation can be observed: allocation per optimization is the favorable auction design when revenue maximization is more important than fair allocation. On the other hand, pro rata allocation is the auction design to be chosen when fairness of allocation is considered most central. (C) 2011 Elsevier Ltd. All rights reserved.