Reading maintained their promotion charge with an emphatic win at Oakwell to secure their ninth win in 10 games.
After a goalless first half, strikes from Jobi McAnuff and Jem Karacan set the Royals on their way to victory within minutes of the restart.
Karacan added a brilliant third from long range in the 65th minute, while the prolific Jason Roberts completed the rout with a smart finish late on.
It moves Reading three points clear of third-placed West Ham, who drew.
But it leaves Barnsley on the fringes of the relegation fight after a run of six games without a win.
Their form is in sharp contrast to Reading, who had won eight games on the trot before their midweek draw at Doncaster.
A repeat of that outcome looked on the cards when Brian McDermott's side failed to break the deadlock in the first half, even if it was mainly down to Barnsley keeper Luke Steele that the scores remained level.
He did well to deny Noel Hunt from a tight angle after just 45 seconds before making superb saves from Roberts and Mikele Leigertwood.
But Reading were ahead in the 47th minute when Roberts laid the ball off for McAnuff to hit a low drive from the edge of the box.
Two minutes later, Barnsley failed to clear a ball in the penalty area and Karacan lashed in from 12 yards.
Karacan added a third with a blistering 25-yard strike before Roberts completed the scoring in the 90th minute after good work from Alex Pearce.
Barnsley manager Keith Hill: "I believe that we are in a relegation fight because the confidence is low. When you lose two early goals in the second half the players' confidence goes.
"At the moment we are in poor form. In fact we are in relegation form. We've got to show bravery and I expect my players to show bravery.
"I thought that in the first half we were more than competitive and we came up against a good side. I think Reading are the most effective side that we have played.""
Reading manager Brian McDermott: "To come to a tough place like Barnsley and win 4-0, I can't ask any more of my players.
"It was tough in the first half; I've not seen a team play as well and come at us like they did. They upset our rhythm and had a couple of early chances.
"There was no need for any harsh words at half-time. I knew that if we got the ball down and passed it that we would score."