Thanks to an eye-catching run of form, the visitors have climbed to ninth spot in the third-tier table and within eight points of their fifth-placed hosts.
Match preview
Barnsley will return to Oakwell on Saturday with the aim of bouncing back to winning ways and strengthening their position in the top six in League One, having seen an eye-catching run of form come to an end in recent weeks.
In their bid to win promotion back to the Championship this term, the Yorkshire outfit shone between late November and late January, going 11 games unbeaten including seven victories to move onto 52 points from 27 outings.
That streak, culminating in consecutive wins over Bristol Rovers, Carlisle United and Oxford United, left Neill Collins's side firstly in the automatic promotion fight, but they have since seen their momentum halted slightly, firstly losing their unbeaten run in a 2-1 defeat at home to Exeter City at the end of January.
In their bid to make a swift return to winning ways, the Reds most recently faced a tough trip to fellow promotion-chasers Bolton Wanderers last weekend, and they were able to at least leave with a creditable point from a 1-1 draw, having gone ahead early on through Devante Cole inside five minutes before Zac Ashworth levelled the scores around the hour mark.
Now sitting six points outside the top two, with a game in hand on second-placed Derby County but having played a game more than third-placed Bolton, while now only leading seventh-placed Oxford United by two points, Barnsley are entering a decisive period in their promotion bid and will set out to build another run beginning with a home victory at the weekend.
In their way stand a Leyton Orient side who arrive at Oakwell as one of the league's form teams in their own surprise top-six push this term.
After only winning promotion from League Two last season, Richie Wellens's side have enjoyed an impressive campaign in England's third tier thus far, currently sitting ninth with 45 points on the board from their opening 30 outings.
That is in no small part down to an impressive run of form since Christmas, with the Os having gone unbeaten in their last eight matches while picking up six victories, including three straight triumphs over Cambridge United, league leaders Portsmouth and third-placed Bolton Wanderers to begin the New Year, scoring six times across those games without conceding.
After then taking a creditable point from a 1-1 draw away at Reading, Wellens's men head into Saturday's trip on the back of another pair of consecutive three-point hauls, beating Carlisle United 3-2 at home last weekend and prevailing away at Port Vale on Tuesday as Idris El Mizouni hit the only goal of the game on the hour mark.
Having quickly moved into the playoff picture thanks to their eye-catching hot streak, Leyton Orient now trail sixth-placed Stevenage by seven points and Saturday's hosts by eight points, and they will be desperate to continue building momentum and further improve their hopes with a third straight triumph at the weekend.
Barnsley League One form:
D
W
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L
D
Leyton Orient League One form:
W
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D
W
W
Team News
With defender Jamie McCart likely remaining their only absentee through injury, Barnsley may come into Saturday's contest with an unchanged starting XI from their draw away at Bolton Wanderers last time out in a 3-5-2 shape.
In McCart's absence, January arrival Josh Earl should again join Mael de Gevigney and Jordan Williams in a back three, while Barry Cotter will hope to keep his starting spot on the right-hand side after getting the nod over Corey O'Keefe last time out.
Elsewhere, Luca Connell, Adam Phillips and Herbie Kane are bound to continue in the midfield, while John McAtee should again star man Devante Cole up front, with the latter having notched up a league-high tally of 17 third-tier goals so far this term.
Leyton Orient should also be unaltered from their latest outing on the back of a second straight League One victory away at Port Vale, with key defender Omar Beckles again set to miss out through injury alongside winger Jordan Graham.
In Beckles's absence, Dan Happe and Brandon Cooper are bound to continue their partnership in the middle of a back four after Tuesday's clean sheet, while Idris El Mizouni and Jordan Brown are mainstays in midfield.
Ahead of them, Shaqai Forde, George Moncur and Theo Archibald will likely line up in an unaltered supporting trio behind lone striker Ruel Sotiriou, who sits level with Forde at the top of the Os' scoring charts with eight goals this term.
Barnsley possible starting lineup:
Roberts; Williams, De Gevigney, Earl; Cotter, Phillips, Connell, Kane, Cadden; McAtee, Cole
Leyton Orient possible starting lineup:
Brynn; Galbraith, Happe, Cooper, James; Brown, El Mizouni; Forde, Moncur, Archibald; Sotiriou