The two sides are in different divisions, but there does not seem to be much separating them going into the match.
It is shaping up to be quite a season for Oxford as they are one win away from a trophy tomorrow and in contention to go up from League Two.
With Northampton Town 14 clear at the top, it seems that there are just two automatic promotion places to fight for and with only six games of the season remaining, it is Oxford leading the pack at the moment.
Appleton's men have suffered defeat just once in their last nine games and they are unbeaten in their last four, although the last two have both been draws.
They are in the final of the Football League Trophy for the first time thanks to wins over Swindon Town, Dagenham & Redbridge and Yeovil Town before they overcame Millwall 2-1 in the two-legged semi-final courtesy of a 2-0 away win in the first leg.
As well as their run in the Johnstone's Paint Trophy, Oxford also wrote some headlines in January when they upset Premier League side Swansea City in the FA Cup.
Recent form: DLWWDD
Most of Barnsley's good work in the competition this season came under the guidance of Lee Johnson, but Bristol City recognised his good work and poached him in February just after the Tykes reached the final.
The Tykes have won seven of 11 under Heckingbottom, losing just twice in that time and keeping clean sheets in their last three games to lie seventh in the third tier, four points behind the playoffs but with a game in hand.
Like Oxford, Barnsley are in the final for the first time after scraping through the last two rounds on penalties.
Three 2-1 wins over Scunthorpe United, Bradford City and York City got the Tykes to the last eight before they needed penalties to beat Wigan Athletic, going on to also come past Fleetwood Town in a shootout after a pair of 1-1 draws in the semis.
Recent form: WWLWDW
Oxford possible starting lineup:
Buchel; Long, Wright, Dunkley, Ashby; MacDonald, Sercombe, Ruffles, Maguire; Roofe, Bowery
Barnsley possible starting lineup:
Davies; Williams, Roberts, Mawson, White; Scowen, Brownhill, Hourihane, Hammill; Winnall, Toney
Head To Head
Sunday's contest will be the first meeting between the two in over 17 years. They last clashed at the Manor Ground in January 1999 when a 60th-minute strike from Dean Windass was enough to clinch a 1-0 victory for United.
In total, the U's and Tykes have met on 22 occasions, with Barnsley holding the advantage with ten wins to Oxford's seven.
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We say: Oxford 2-2 Barnsley
It really is difficult to separate these two sides and Oxford's cup prowess this season might just be enough to earn them a victory in extra time or on penalties.