Oslo-listed Subsea 7 is looking to buy the 50% it does not own in Seaway Heavy Lifting.
The stock is owned by K&S Baltic Offshore and would bring its ownership to 100%.
The offer is open until 1 July, during which period Seaway's works council in the Netherlands will be consulted over the move.
Subsea 7 CEO Jean Cahuzac said: "Subsea 7's strong market position in offshore energy services is complemented by Seaway Heavy Lifting's expertise in three areas of offshore activity: renewables, heavy lifting operations and decommissioning of oil and gas assets.
"We
