Crossrail has advertised the third and final tunnel contract, C310, for the £15.9bn project.
C310 involves the construction of twin 6.2m diameter bored tunnels from Plumstead Portal to North Woolwich Portal.
The length of each drive is approximately 2.6 km.
The deadline for expressions is 24 March 2010.
Crossrail chief executive Rob Holden said: “This is an important day for the programme. The invitation to express interest in the Thames Tunnel contract means that we are progressing with the procurement of all three running tunnels contracts. It is another significant step towards delivering Crossrail on time and to budget.”