Cash could be outlawed on London's buses by the end of the year, according to a Transport for London document obtained by the BBC.
With the Oyster card now dominant on London's transport network, just 1.5% of bus fares - 24 million journeys a year - are paid for with cash.
This figure is expected to fall further thanks to the introduction earlier this year of an option for commuters to pay using contactless bank cards.
TfL now wants to ditch expensive cash completely by the end of the year, writing in a confidential Mayoral briefing paper seen by the BBC: "It is also proposed that the sale of cash tickets on bus be stopped at a suitable time in 2013."
Managing director for surface transport at TfL Leon Daniels told the BBC that "we've made no decision on this whatsoever" but added that "we are watching the market" and "there will come a point when it won't be worth collecting cash anymore".
Any decision on ditching notes and coins will ultimately be made by London's Mayor, Boris Johnson.