Federal judge Richard Matsch said in court that the jury had told him it could not reach a unanimous decision on Nichols' intentions.
The jury convicted Nichols last month of conspiracy and involuntary manslaughter in the April 19, 1995 attack that killed 168 people.
The jury's failure to reach a unanimous decision effectively spared Nichols the death penalty handed to his co-conspirator, Timothy McVeigh, last June. Unlike the jury, Judge Matsch does not have the power to impose a death sentence.
He said he would not set a date for a sentencing hearing until he had heard submissions from both the defence and prosecution lawyers, which he told them to make by 9 February. Judge Matsch can imprison Nichols for life or choose a shorter sentence.
Jurors, clearly strained by their task - two of them cried in court on Tuesday, including the forewoman - told the judge at the end of the day that they could not reach a decision. He did not announce this until court opened yesterday.
Judge Matsch told the jurors that they had done their job. "I do not want you to feel that you have in any way failed to meet your responsibility," he said.
A bank clerk on the jury cried and others looked dejected.
Nichols sat expressionless, but after the jury left the room he smiled and hugged one of his lawyers. Another lawyer patted him on the back.
"I guess that's what we hoped and prayed for," said Nichols' sister, Suzanne McDonnell.
McVeigh was convicted of all charges in the bombing of a federal office building in Oklahoma City, an attack that stunned America.
But Nichols was acquitted of murder and of carrying out the attack. He faced the death penalty only for the conspiracy charge.
Reuters, DenverReuse content