Despite an apparent abundance of supply, high securities borrowing costs on stocks show that demand can easily exceed supply when corporate actions or thinly traded securities are involved.

A survey of 31 large global institutions, published last month by the International Corporate Governance Network, a lobby group, showed 28 had never lent more than half their portfolio at any time. This suggests there is plenty of capacity for borrowers. However, prime brokers say this can quickly disappear and they would welcome more lenders.