Why does my cylinder feel light?

One reason may be that it is empty! To find out how to tell if this is the case, see 'How can I tell if a cylinder is empty?'.

However, BOC Sureserve uses two types of cylinders: steel and aluminium. An aluminium cylinder may feel lighter than usual because it will weigh less than a steel cylinder of the same size. But the gas content is exactly the same, size for size.