Gatwick could be handling 40 million passengers a year by 2021/22 and around 45 million by 2030, the West Sussex airport's bosses said today.
Under a long-standing local agreement, a second runway at Gatwick, which currently handles around 34 million passengers a year, cannot be built before 2019.
In a masterplan for the airport today, Gatwick chiefs said they remained committed to honouring this agreement.
But chief executive Stewart Wingate added: "At the same time, and like any other business, our plans need to cater for all eventualities.
"We need to anticipate that, in the long term, a second runway at Gatwick may be needed. This means we will continue to work in partnership with our local authorities to safeguard land for future expansion because we believe it to be sensible business practice and it supports current Government policy."
The Government had been due to publish a consultation on UK airport capacity requirements in March, but this was postponed until the summer and last week it was postponed again - this time until the autumn.
In its masterplan today, Gatwick said it planned to invest a further £1 billion in the airport from 2014 and that growth to 40 million passengers by 2021/22 would create 1,200 on-airport jobs and contribute around £2.1 billion to the regional economy each year.
The airport would be full by 2030.
Gatwick chiefs said a noise insulation scheme for local residents already existed and a new scheme would be rolled out in 2013 following a public consultation.