Whereas the assured pays a premium to an underwriter for cover which lasts for a particular time (say, a year, or a voyage), a P&I club member instead pays a "call". This is a sum of money that is put into the club's pool, a kind of "kitty". If, at the end of the year, there are still funds in the pool, each member will pay a reduced call the following year; but if the club has made a major payout (say, after an oil spillage) club members will immediately have to pay a further call to replenish the pool.