The warmest parts of the Underground network have been revealed in a map compiled by Transport for London (TfL).
The Central Line was the hottest, with temperatures of 32C (90F) between Holland Park and Mile End.
Most stations on the Bakerloo Line reached 32C, though temperatures eased further south on the line.
The map covers most Underground lines in zones one and two between 1600 BST and 1900 BST on 28 July last year - the hottest day of the year.
The Jubilee Line was significantly cooler with most stations recording temperatures of 25C (77F).
Map reveals hottest parts of Tube
The map has been used by TfL for years to help officials monitor temperature levels on the network.
"Cooling the Tube is one of the greatest engineering challenges faced by London Underground (LU)," said a TfL spokesman.
"It is a programme that will take years, not months, to deliver results."
Millions of pounds were being invested to tackle heat across the network, he said.
This includes the delivery of new air-conditioned trains on the Metropolitan Line from 2010, the Circle, Hammersmith and City lines from 2011 and District Line from 2013.
Other initiatives include upgrading out-of-service ventilation shafts and a ground water cooling trial that started at Victoria station in Summer 2006.
LU has long struggled with how to reduce heat in narrow Tube tunnels - some of which were built more than a century ago.