They were Sarah Darnley, 45, from Elgin - the first woman to die in an offshore North Sea accident; Gary McCrossan, from Inverness; Duncan Munro, 46, from Bishop Auckland; and George Allison, 57, from Winchester. The bodies of three of four victims have so far been recovered, and rescuers are now working to locate the body of the final missing victim. It is not clear which victim has yet to be found.
Last night, the parents of Sarah Darnley, who worked as a steward for a catering company for more than 20 years and travelled the world with her job, spoke of their agony at not knowing if their daughter's body has yet been found.
Her 81-year-old father Edmund and mother Anne, 73, said: "The worst is not knowing - the waiting is terrible. When we first heard about the accident, we tried to get hold of her by phone, text and email. But we could not get through to her. Our worst nightmare came true at 11.30pm on Friday night when a policeman came to the door to tell us Sarah had been killed. We believe the bodies were trapped in the wreckage and one has not been found. No-one is able to tell us yet if it is Sarah."
In a further statement, her mother added: "We are shocked by the sudden loss of Sarah, who was a fun-loving free spirit who will be sorely missed. Sarah was born and brought up in the Elgin area. She attended Elgin High School and moved to Aberdeen when she was 19.
"She enjoyed her job. She had great camaraderie with her colleagues and over the years she made some fantastic friends whom she was able to visit in various parts of the world, including South America and Thailand.
"Sarah lived life to the full, she was easy going and a one-off. She will be deeply missed by all who knew her."
Sarah's sister, Angela, said: "She loved her work. She was passionate about it and never expressed any fears about travelling in helicopters despite the dreadful previous incidents.
"She simply put it to the back of her mind. She had complete faith in them. Working offshore enabled her to pursue her love of travelling. She worked in the Falkland Islands, the Congo and Turkey, as well as the North Sea.
"We last spoke to her on Tuesday after she had been three weeks away. Sarah was doing relief work and had been on many different rigs, but she had worked on this one for some time.
"She was about to go on holiday to Spain to visit her friend there, and had been learning Spanish.
"No-one has given us any details. The only information we have been getting is what has been on the news.
"Her company sent someone up last night to see us which was very nice of them and we expect them or the police to keep us informed."
Duncan Munro's family issued a statement saying: "Duncan was a fabulous father to Katy, aged 12 years, and a devoted husband to Penny. He was a loving brother and a good friend and colleague to many.
"He will be sadly missed by everyone that knew him and his death will leave a large void in a lot of people's lives.
"His family would like to thank everyone for their kindness and support since they received the tragic news, they would also like to pass on their sincere condolences to the other families who have lost loved ones in this tragic incident."
Amanda Smith, whose son Sam was on the helicopter, said the aircraft suddenly lost power and those on board had "no time to brace".
"He was by the window so he was able to escape that way as it rolled over," she said. "He said he had come off better than a lot of people, [those] were his words."
Michael Bull, whose son Samuel was rescued, said: "We understand he was on his way back from a rig and the helicopter lost power suddenly and immediately ditched into the water.
"He managed to escape straight away because he was right by an exit and I understand soon afterwards that the helicopter turned over."
Scotland's First Minister, Alex Salmond, said his thoughts were with the relatives of those who died, and he wished the injured a "full and speedy recovery".
He added: "I would like to pay a massive tribute to all of those brave and hard-working individuals involved in the rescue effort and in treating the casualties when they were brought ashore.
"It is still too early to know what caused this terrible tragedy, but a full investigation by the relevant authorities is already under way."