They have entered into a merger implementation deed under which they will merge via a Horizon scheme of arrangement to form a single Asian-centric company.
Horizon shareholders will receive 0.724 Roc shares for every Horizon share they hold. That means Roc shareholders will own about 42% of the merged entity and Horizon shareholders get the rest.
Both companies' boards have supported the merger unanimously, with the board of Horizon strongly recommending it shareholders vote in favour of the merger.
The merged company will have a pro forma market capitalisation of about $800 million, net 2P and 2C reserves of 36.9 million barrels of oil equivalent and 102.7MMboe respectively.
The scope of the combined entity's work in the Asia Pacific will cover China, PNG, Malaysia, Myanmar, Australia and New Zealand.
"This is a transformational and exciting transaction and something ROC has been working towards for some time," Roc chairman Mike Harding said.
"The combination of our companies will create a high calibre operating company with the capacity to actively progress value-adding growth through a combination of existing material development projects, complemented by a portfolio of high impact and low risk exploration assets within our core operating regions.
"Consolidation of the ASX-listed exploration and production sector has been well-flagged but slow to occur. This transaction represents a unique and compelling opportunity to bring together two companies with highly complementary assets to create a new Asian-focused mid cap exploration and production champion."
The merged board of the companies will comprise three non-executive directors of Roc and four non-executive directors of Horizon, with Horizon CEO Brent Emmett heading the new company as CEO and managing director.
Harding will continue on as chairman of the combined board, and Roc CEO Alan Linn will become president of the merged group.
The MID is conditional on a number of factors, including Horizon completing its $US77 million ($A81.9 million) sale of 40% of its PNG asset to Japan's Osaka Gas and it gaining 75% approval of votes cast by its shareholders.
