Former 'Daily Mirror' reporter Graham Brough and the 'Sun' tabloid's Neil Millard, Brandon Malinsky and Tom Wells were cleared of "conspiring to commit misconduct in public office" by a jury at the Old Bailey court.
The UK Crown Prosecution Service (CPS) has been given seven days to decide whether to seek a retrial on two remaining counts.
Millard, 33, Malinsky, 50, Brough, 54, and Wells, 34, had all denied charges of paying prison officials for stories.
The trial is part of Scotland Yard's Operation Elveden into allegations of inappropriate payments to police and public officials.
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Speaking outside court, Millard said his heart had been "pounding and pounding" while standing in the dock as the verdicts were read out.
"I did not expect, when I went to do shifts at the 'Sun', that I would end up at the Old Bailey on the three counts on an indictable offence," he said.
The four journalists are the latest reporters to have been tried on charges brought under Operation Elveden.
All of them had denied various counts of conspiring to commit misconduct in a public office and bribing public officers in return for information for their newspaper reports.
The controversial police investigation into newspapers' dealings with public officials is believed to have cost an estimated 20 million pounds.
So far two journalists have been convicted following a trial - a 'News of the World' reporter who cannot be named, and another Ryan Sabey, who has been given leave to appeal.
Thirteen journalists have been acquitted.