Stansted Runway south of the existing one between the villages of Takeley and Molehill Green.
For: Front runner. Less contentious than Heathrow and Gatwick because it would have less environmental impact.
Case could be strengthened by situating check in facilities in the Thames Gateway area of east London, aiding urban regeneration.
Against: Strong opposition from county council and local people.
Heathrow Between the M4 and A4 near Harmsworth, requiring demolition of about 100 houses. Shorter runway for smaller craft, freeing up capacity for larger planes on the existing strips.
For: High demand from public to use Heathrow. No legal impediment to building a new strip. Although T5 public inquiry inspector Roy Vandermeer recommended against it, and BAA said it didn't want it, the government is not legally bound by his report.
Against: Strong legal challenge highly likely.
Gatwick New runway in open countryside 3km north of existing terminals near village of Charlwood.
For: Busiest single runway airport in the world, strong demand for extra capacity.
Against: East Sussex County Council claims legal agreement blocking expansion until 2019 although government lawyers are probing this agreement.
New airports Manston Former military airstrip near Ramsgate which has gained its CAA licence.
For: Long runway of 2.75km.
Surface friction problem has been solved after 20mm porous asphalt friction wearing course was laid.
Could be linked with Channel Tunnel Rail Link (CTRL) at Ashford 40km away.
Against: Distance - 125km from London.
Thames estuary Proposals include resurrecting Maplin Sands proposal near Southend, identifying a new site near Dartford or even building an artificial island to site an aiport in the Thames estuary.
For: Thames Gateway regeneration. Could link into CTRL or Crossrail.
Against: Much of the estuary area is protected for birds and other wildlife.
Didcot New Heathrow-sized airport on farmland near Didcot. Two 4km runways with 80M-100M capacity developed by Ove Arup and architectural practice Pleaide Associates in the early 1990s.
For: Near to M4, M40 and Great West Main Line.
Against: Opposition from nearby residents in powerful commuter belt area.