There now exist several alternatives to cork as wine bottle closures. The emergence of alternative closures with consistent physical properties has focused attention on the science of post-bottling wine chemistry. While much research in this area remains undone, it is clear that oxygen transmission by the closure has a significant impact on how wines develop after bottling. The role of closure oxygen transmission is an area of active research, and the potential of matching closure type to wine style is now being discussed by winemakers. As well as oxygen transmission, closures differ in their capacity to scalp flavour compounds from wine. Other issues relating to closure choice include cost and consumer acceptance. While cork remains the dominant closure for wine, screwcaps and synthetic corks have now taken significant slices of the bottled wine market (estimated 2.5 billion and 3.7 billion units used annually).