William Hill has confirmed odds of 4/1 for both Hawley's Standing At The Sky's Edge and Plan B's Ill Manors.
"You couldn't have a more diverse pair of favourites, but therein lies the beauty of the Mercury Prize," said Joe Crilly, a spokesman for the bookmakers.
"While Plan B and Richard Hawley currently head the betting, there will undoubtedly be a fair few movements in the market between now and November 1."
Newcomers Alt-J and Django Django are given odds of 5/1 by William Hill for their respective debuts An Awesome Wave and Django Django.
However, Alt-J are named as 6/4 favourites for the accolade by Paddy Power, with Hawley at 11/2 and Plan B a relative outsider at 16/1.
Alt-J are also favourites with Sky Bet, who have given the quartet odds of 7/4.
The Barclaycard Mercury Prize will be awarded on November 1 during an awards ceremony at the Roundhouse in London.
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Photo gallery - Mercury Prize 2012: Nominees in pictures:
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