The news follows the re-signings of Dan Parks, Sam Pinder, Steve Swindall, Fergus Thomson, Eric Milligan and James Eddie in the past week and a half, as well as the confirmation that Dougie Hall, Ed Kalman and Richie Vernon will move to the Warriors from Scotland's other two pro-teams ahead of next season. Further player announcements will follow in due course.
A six-times capped international centre, Morrison first signed with Glasgow in season 2003-04 and has been a regular fixture in the side's backline since moving from Glasgow Hawks. Former Welsh rugby league international O'Hare first signed for the club in 2005, having made the switch to rugby union where he fits comfortably either on the wing, in the centre or at fullback. Gregor is a former Scotland 7s star, winning 17 sevens caps before turning professional with Glasgow for the 2005-06 season.
On the three players, coach Sean Lineen said: "Graeme has been with us for a few seasons now but he has got a big year coming up with us and internationally, having earned a place in the Scotland 'A' Barclays Churchill Cup training squad this summer. He's an intimidating player and I'm looking for him to grab the bull by the horns and deliver his best rugby in the coming seasons.
"Hefin has been a revelation this season and if everyone had a heart the size of his we'd be unstoppable. He always gives 100% and his work ethic is phenomenal so he's a great player to have in your squad. He's among the Magners League's top try scorers this season and this announcement comes in recognition of his achievements.
"Colin is another fantastic re-signing for us. He has lived partly in the shadow of Dan Parks this year and has paid a small price for his versatility but there are opportunities ahead while Dan is in France for the World Cup in the autumn. It's exciting to watch a player like Colin control a backline and show off his obvious skill with the ball," he added.