Posh were 16-1 with Sky Bet when that firm published their first title odds in the middle of May. Those idds have now been halved.
After Posh come MK Dons (10-1) and Derby County (11-1) with Fleetwood Town and Morecambe the rank outsiders at 150-1.
Posh are 9-4 to win promotion, 7/2 to finish in an automatic promotion place, odds on at 5/6 to finish in the top 6.
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Posh are also 5-1 joint second favourites with Ipswich Town to score the most League One goals. Wednesday are 4-1 favourites.
Full Sky Bet League One title odds: 4-1 Sheffield Wednesday, 9-2 Ipswich, 8-1 POSH, 10-1 MK Dons, 11-1 Derby, 12-1 Barnsley, Bolton, Portsmouth, 14-1 Oxford, Wycombe, 22-1 Plymouth, 25-1 Charlton, 50-1 Lincoln, Shrewsbury, 66-1 Accrington, Burton, Bristol Rovers, Forest Green, 80-1 Cambridge, Cheltenham, Port Vale, 100-1 Exeter, 150-1 Fleetwood, Morecambe.