A wet lease is a leasing arrangement whereby one airline (lessor) provides an aircraft, complete crew, maintenance, and insurance (ACMI) to another airline (lessee), which pays by hours operated. The lessee provides fuel and covers airport fees, and any other duties, taxes, etc. The flight uses the flight number of the lessee. A wet lease generally lasts one month to two years; anything less would be considered an ad-hoc charter. A wet lease is typically utilized during peak traffic seasons or annual heavy maintenance checks, or to initiate new routes, a wet leased aircraft may be used to fly services into countries where the lessee is banned from operating.
They can also be considered as a form of charter whereby the lessor provides minimum operating services, including ACMI, and the lessee provides the balance of services along with flight numbers. In all other forms of charter, the lessor provides the flight numbers. Variations of a wet lease include a code share arrangement and a block seat agreement