Oxford are dreaming of ending their 25-year wait for second-tier football, while Posh are looking to return to the Championship after spending the last two seasons in League One.
Match preview
Oxford are set to appear in the League One playoffs for the first time since losing to Blackpool in the 2020-21 semi-finals.
The U's leapt from seventh to fifth spot on the final day of the season after they beat Exeter City 2-1 to take advantage of Lincoln City's defeat to Portsmouth and Barnsley's draw with Northampton Town.
Mark Harris and Cameron Brannagan grabbed a goal apiece in the first period to edge out the Grecians and extend Oxford's unbeaten away run to four matches.
After enjoying away-day success, the U's will now return to the Kassam Stadium, where they have failed to win their last two matches after following a defeat to Lincoln City with a draw against Stevenage.
However, Oxford can certainly take confidence from the fact their most recent home victory took place against Peterborough earlier this month.
On that occasion, the U's produced a free-scoring display to cruise to a 5-0 victory, which represented their first head-to-head win since August 2019.
Peterborough are set to compete in the League One playoffs for a second straight season after they collected 84 points to finish in fourth and seven points ahead of Saturday's opponents.
Despite achieving a top-six finish, Darren Ferguson's side experienced an inconsistent end to the campaign, with their final five matches producing two wins, one draw and two defeats.
They looked set to claim three points in their final match of the season, as they fought back from two goals down to take a 3-2 lead against third-placed Bolton Wanderers following a Malik Mothersille brace and a Joel Randall effort.
However, Bolton's Cameron Jerome came off the bench to net an 82nd-minute equaliser to deny Peterborough a fourth consecutive home win.
Peterborough will still be scarred by last season's playoff campaign, where they gave up a 4-1 first-leg lead against Sheffield Wednesday to lose 5-1 after extra time in the away leg.
If they are to make the final this time around, Posh will need to provide the sort of attacking threat that saw them finish the season as the league's highest scorers with 89 goals in 46 matches.
Oxford United League One form:
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Peterborough United League One form:
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D
Team News
Oxford are hopeful that Will Goodwin will be available for selection after being without the forward since the middle of March.
Defender Sam Long missed the win over Exeter through illness, but he could return to the starting lineup for Saturday's first leg.
Harris will be given the responsibility of leading the line after scoring six goals in the final six matches of the League One season.
As for the visitors, Jeando Fuchs will miss both legs with a knee injury, but he is making progress in his recovery and could be available for the final if Peterborough are able to secure their place at Wembley.
Ferguson is expected to select the same lineup that started the 3-3 draw against Bolton, which would see Mothersille operate as the sole centre-forward with attacking support offered by David Ajiboye, Ephron Mason-Clark and Randall.
Michael Olakigbe will provide an option off the bench after he returned from a six-game injury absence to feature in last Saturday's matchday squad.
Oxford United possible starting lineup:
Cumming; Long, Moore, Brown, Bennett; Dale, Rodrigues, Brannagan, Goodrham, Murphy; Harris
Peterborough United possible starting lineup:
Steer; Katongo, Knight, Edwards, Burrows; Kyprianou, Collins; Ajiboye, Randall, Mason-Clark; Mothersille