The Ocean Tay is a Class A emergency response and rescue vessel, which will provide emergency vessel cover for Nexen's flagship Golden Eagle Area development in the North Sea.
The charter will last a minimum of two years.
Atlantic Offshore Rescue is part of the Norway-based Atlantic Offshore Group.
It provides multi-role offshore and emergency rescue and response vessels for many of the oil majors operating in the North Sea.
The Ocean Tay underwent conversion at Wear Dock & Engineering in Sunderland to become one of a fleet of 12 ERRVs AOR manages out of Aberdeen.
The 63m vessel can accommodate a crew of 20 and rescue more than 300 people.
AOR has invested about £300 million in its fleet modernisation program in the past three years.
The Ocean Tay is the second high-specification ERRV the company has commissioned in recent months.
The first, the Ocean Troll, is the UK's most powerful ERRV and is AOR's principal relief vessel.
AOR has another two ERRV/tanker assist vessels under construction for delivery in 2014 and 2015.
Besides AOR's 12 vessels, Atlantic Offshore Group operates a fleet of 24 ERRVs and platform support vessels and manages other PSVs on behalf of third parties.