The Williamses' biggest challengers for an Olympic gold figures to be Liezel Huber and Lisa Raymond or Sara Errani and Roberta Vinci.
WTA Staff

LONDON, England - The Williams sisters, Liezel Huber and Lisa Raymond and Sara Errani and Roberta Vinci are the gold medal favorites in the doubles competition that begins Saturday at the All-England Club.

Serena and Venus Williams are 10-0 as an Olympic duo, collecting gold medals at Sydney in 2000 and Beijing in 2008. On top of that, in their first doubles tournament in two years at Wimbledon earlier this month, they netted their fifth title there and 13th career major and in the process raised their overall record to 154-19 and grass court record to 38-2.

Another pair representing the US is World No.1s, reigning US Open champions and No.1 seeds Huber and Raymond. They netted consecutive titles in Paris, Doha, Dubai and Indian Wells earlier this year, however, have not returned to the winner's circle since. They did have a strong grass court season, with runner-up showings in Birmingham and Eastbourne and a semifinal outing at Wimbledon. And although they have three Olympic experiences between them, so far a medal has eluded each.

Errani and Vinci are a remarkable 43-5 during a year that has included a 25-match win streak, the longest by a duo since Gigi Fernández and Natasha Zvereva won 28 in a row in 1994. The second-seeded Italians also have a WTA-best seven titles, highlighted by their first Grand Slam at the French Open, and lead the race to qualify for the TEB BNP Paribas WTA Championships - Istanbul 2012 by a wide margin.

Others who could be a threat include third-seeded Russians Maria Kirilenko and Nadia Petrova and fourth-seeded Czechs Andrea Hlavackova and Lucie Hradecka. Kirilenko and Petrova's season has included a title in Miami and a run to the final at Roland Garros. Third in the race to Istanbul standings, Hlavackova and Hradecka have two titles in 2012 and proved their grass court prowess with a runner-up showing at Wimbledon.

(7) Pennetta/Schiavone (ITA): They had their best major as a duo earlier this month in reaching the semifinals at Wimbledon.
(8) Llagostera Vives/Martínez Sánchez (ESP): They netted their 10th title together in Eastbourne last month.
Dulko/Suárez (ARG): Suárez, a 2004 bronze medalist with Patricia Tarabini, was motivated to return to the WTA this year for a shot at a medal in London.
Medina Garrigues/Parra Santonja (ESP): Medina Garrigues was a silver medalist in 2008 alongside Virginia Ruano Pascual.
Peng/Zheng (CHN): Zheng was a bronze medalist in 2008 alongside Yan Zi.