Another factor in the growth of subscription libraries was the increasing cost of books. In the last two decades of the century, especially, prices were practically doubled, so that a quarto work cost a guinea, an octavo 10 shillings or 12 shillings, and a duodecimo cost 4 shillings per volume. Price apart, moreover, books were difficult to procure outside London, since local booksellers could not afford to carry large stocks. Commercial libraries, since they were usually associated with booksellers, and also since they had a greater number of patrons, were able to accumulate greater numbers of books. The United Public Library was said to have a collection of some 52,000 volumes-–twice as many as any private-subscription library in the country at that period. These libraries, since they functioned as a business, also lent books to non-subscribers on a per-book system.