The three had initially said that they were innocent of colluding with Fastow and attempted to prevent their extradition from the UK to the US for trial.
They said that they should have been tried in the UK, as the alleged fraud took place there against a British bank, now a unit of the Royal Bank of Scotland Group Plc.
As a US-British extradition treaty had not been ratified by the US congress at the time, the UK government came under significant pressure.
The treaty was ratified after lobbying from UK officials and the three bankers were extradited in July 2006.
In November they each pleaded guilty and signed a plea agreement. This deal stated that they had advised NatWest to sell an offshore Enron-related firm for less than its real value.
They then brought the stake in the company with Fastow's assistance and resold it for a $19 million profit.
The trio's share of that profit amounted to $7.3 million between them. They have agreed to forfeit the stolen money to Natwest.
The three, all 45, have been released on bond until a date is set for them to report to prison.
They have all said that they will apply to serve their sentences in the UK.
Enron collapsed in 2001 after declaring bankruptcy with billions of debt.
Fastow is already serving a six year sentence for his part in the accounting scandal which led to the fall of Enron.