"O'May rules"
The principle that the terms of a new lease, will generally follow the terms of the existing one; the onus is on the party proposing a change to show that it is fair and reasonable (O'May v City of London Real Property Co Ltd, 1983).

Off-balance sheet finance
Financial techniques which allow companies to incur debt, usually via associated companies or joint ventures, without the debt appearing in the group's consolidated accounts and affecting its gearing ratio.

Open market rent
See market rent.

Open market rent review
Where the rent review clause provides that the rent on review should be based on the open market prevailing for new lettings.

Over-renting
This occurs when the rent passing exceeds the current open market rent

Overriding lease
An intermediate lease which the landlord grants to another party for a term longer than that of an existing lease, thereby creating a landlord and tenant, but not a contractual, relationship between the new and old lessee.