This study details molecular dynamics simulations for the formation of ethane clathrate hydrates. Ethane hydrate nucleation shares with methane hydrate nucleation the formation of coordinated guest clusters in water, resulting in structures such as guest-saturated pentagonal and hexagonal faces. Ethane hydrate also forms structure I, which consists of two 5(12) and six 5(12)6(2) cages in its unit cell. Observations from the simulations reveal differences between methane and ethane in the nucleation process, including the types and occupancies of cages. While the formation of occupied 5(12) cages dominates methane hydrate nucleation, nucleation of ethane hydrates predominately exhibits the 4(1)5(10)6(2) cage as both the first and most common early cage type. These 4(1)5(10)6(2) cages do not occur in the crystal structure, and due to their oblong shape, restrict the orientation of the coordinated guest ethane molecule. The initial kinetically favored 4(1)5(10)6(2) cages are observed to undergo transformation into different cage types, such as the thermodynamically favored 5(12)6(2) cage. (C) 2015 Elsevier B.V. All rights reserved.