The pressure on Reds boss Lee Johnson cranked up a significant notch as they slipped to a disastrous eighth straight Sky Bet League One defeat, this time at the hands of Port Vale.
There were boos around Oakwell at the final whistle as the worst league run since 1959 continued in dismal fashion.
The Reds dominated the first period at a wet and miserable Oakwell, but ended up going into the interval behind.
Vale’s goal came five minutes before the interval with what was their only meaningful opportunity of the half.
Michael O’Connor crossed in from the right, and Ajay Leitch-Smith leapt highest to head past Adam Davies.
Before that the Reds had dominated, with Adam Hammill going close early on when his sweetly-struck half-volley was superbly tipped over the crossbar by ‘keeper Jak Alnwick.
George Smith also tested the Vale stopper, while loan front-man Ivan Toney also went close before the visitors struck.
Vale doubled their lead just two minutes after the restart. Adam Yates squared for Sam Foley, and he fired home left-footed into the top corner from 15 yards.
The Reds missed a great chance on the hour mark, with the unmarked Conor Hourihane somehow firing wide from only eight yards.
Lewin Nyatanga headed narrowly wide, before sub Sam Winnall struck in the 78th minute.
After James Bree’s cross wasn’t cleared, Winnall side-footed home from close range.
Hourihane went closest to grabbing a late leveller, but Vale hung on.
Johnson had made a couple of changes to his starting line-up, with one enforced due to Reece Wabara’s suspension. He was replaced by youngster James Bree.
Up front, Simeon Jackson was replaced by Marly Watkins.
Vale boss Rob Page made two changes to his starting XI, with Sam Foley and Adam Yates returning.
Barnsley (4-4-2): Davies; Bree, Mawson, Nyatanga, G Smith; Isgrove, Pearson, Hourihane, Hammill; Toney, Watkins. Subs: Townsend, Winnall, Jackson, Roberts, M Smith, Abbott, Maris.
Port Vale (4-4-2): Alnwick; Yates, McGivern, Duffy, Dickinson; Moore, O’Connor, Grant, Foley; Dodds, Leitch-Smith. Subs: Neal, Streete, Birchall, Ikpeazu, Daniel, Hooper, Kelly.
Referee: Tony Harrington (Cleveland).