Supposing a membrane surrounded an oil droplet, as it does in the cells of plant seeds and in some animal cells. The oil droplet membrane would contain only a layer of phospholipids rather than having two layers or a bilayer since a structure wherein the hydrophobic end of the phospholipids are in contact with the oil droplet membrane which is a hydrocarbon would give more stability than forming a bilayer. A bilayer structure can be seen when phospholipids are in water since the hydrophilic ends would tend to be attracted to water while the hydrophobic ends would find a way to be away from water forming a double layer.
