Tory leadership hopeful Mr Ken Clarke has warned MPs that members want him in the final ballot as he fights elimination tomorrow.
The former British Chancellor is battling right-winger Mr Liam Fox to survive the first knock-out vote of the Parliamentary Party. Both trail favourite Mr David Cameron and former front-runner Mr David Davis by a large margin on MPs' public declarations.
All four delivered an eleventh-hour pitch to backbenchers at a packed meeting also attended by peers in Westminster.
Only around 40 MPs have not said how they will vote and most of those decided long ago whom they were going to back.
However, arm-twisting and entreaties will continue until the poll closes at 5pm on Tuesday. The result will be announced 20 minutes later.
With a handful of declarations between Mr Clarke and Dr Fox every vote may count, while Mr Cameron's team hope to pick off some of those pledged to Mr Davis.
Bookmakers have self-styled "Big Beast" Mr Clarke favourite to go out in the first vote.
After facing MPs he warned there would be "a great deal of ill-feeling" if he did not make the final round and suggested he should face fellow moderate Mr Cameron, saying: "I don't think I will be first out. I actually sense that what the membership want is David Cameron and myself to go forward at the end."
Brochures featuring polls showing Mr Clarke's appeal to voters were being put on MPs' desks by his team following the hustings. However, bookies say that odds on Conservatives winning the next election would also shorten if Mr Cameron triumphs. They would lengthen if Mr Davis or Dr Fox wins.
A row over the shadow education secretary's refusal to say whether he has used hard drugs may have helped rather than hindered Mr Cameron's chances.