Last-minute talks are to take place in a bid to avert a fresh round of Tube strikes next week following a row over London Underground ticket office closures.
Conciliation service Acas said all of the parties involved will meet this Friday.
It comes as members of the Rail, Maritime and Transport union continued the 48-hour walkout which is due to end at 9pm tonight.
A three day strike has been scheduled to take place from 9pm next Monday, unless the talks are able to resolve the row over closure of ticket offices.
Transport for London said all eleven Tube lines had at least a skeleton service today and insisted nine out ten regular commuters had battled into work yesterday on public transport, based on Oyster card readings.
London Underground managing director Mike Brown said: "I'm sorry that Londoners are enduring more disruption today as a result of the RMT's pointless strike action.
“The only sensible course is for the RMT leadership to call off the strikes and get back to working with us to shape the future of the Tube, as the other three unions are doing.”
The union said a survey it commissioned among 1,000 people showed that the vast majority of Londoners did not believe London Mayor Boris Johnson when he said his plans for closing ticket offices and changes to station staffing will improve passenger services.
