South Korean state-run KNOC has been trying for years to dispose of some or all of its North Sea assets to alleviate its high debt levels.
Waldorf is one of a fresh generation of private equity firms buying up production and squeezing producing fields in the ageing North Sea basin from oil majors and other bigger firms.
Dana, bought by KNOC in 2010 for around $2.9 billion including debt, has fields in the Northern and Southern British North Sea, including a 50% stake in the 45,000 barrel of oil equivalent per day (boed) Tolmount gas field.
Dana, which also has assets in the Netherlands and Egypt, had an output of around 47,000 boed and revenues of around 485 million pounds ($547 million) in 2020, according to its website.
The sources put the price tag for the deal at below $1 billion.
In a separate deal, Waldorf also agreed to buy Dutch gas storage and production assets from Abu Dhabi's Taqa, the latter said in a statement on Thursday.
Dana Petroleum and KNOC declined to comment. Waldorf did not immediately respond to a request for comment.
($1 = 0.8866 pounds)
(Reporting by Shadia Nasralla and Ron Bousso, additional reporting by Joyce Lee, Editing by Alexandra Hudson)
