The website allows Oyster users to top up their cards, review their journey history and apply for refunds.
However figures provided by Mayor Boris Johnson to London Assembly member Caroline Pidgeon revealed that the site was unavailable for a total of 225 hours in 2104, up from 88.6 hours the year before.
Of this, 101 hours was planned downtime which the Mayor says was necessary to allow system upgrades and introduce additional features.
Unplanned downtime soared from 34.8 hours in 2013 to 121 hours last year.
With Tube bosses planning to axe 300 Tube ticket offices, Ms Pidgeon says Transport for London “must ensure that a far more reliable website service is being provided” so Londoners can pay for their journeys and manage their cards.
She added: “Over the last year the Oyster online facility was unavailable for the equivalent of 10 full days. It is simply not acceptable for Oyster Online to be unavailable to the public for such long periods of time.”
