HDR has endorsed a $1.47 billion friendly takeover offer from UK oil and gas producer Tullow Oil. Management have recommended the $2.02 offer.
Hardman said the offer represented a 60% premium to the volume-weighted average price of its shares in the week prior to the arrangement.
Tullow is offering a share alternative, which will allow Hardman stock holders to receive 0.22289 new Tullow shares for each Hardman share, to a maximum of 65 million shares.
Hardman chief executive Simon Potter said the share option gave Hardman shareholders the ability to retain exposure to the company's quality assets with the additional leverage offered by a significantly bigger company.
"The board has concluded that Tullow's offer has the value and flexibility to appeal to Hardman's varied shareholder base, and we recommend the offer to our investors," he said in a statement.
London-listed Tullow is one of Europe's largest independent oil and gas producers, with operations in 15 countries and a market capitalization of GBP2.339 billion (A$5.90 billion), the statement said.