Olivia Wilde loves having private karaoke competitions with her fiance Jason SudeikisThe 'Better Living Through Chemistry' star revealed that she and her fiance Jason Sudeikis, 37, enjoy having singing competitions but she prefers to do it privately because she claims he is a much better singer than she is.The 29-year-old beauty told Jay Leno on 'The Tonight Show': "I love karaoke. I do it but I don't do karaoke in front of other people, I do private karaoke. I get a private room and I just sing along or sometimes with a buddy and he'll just sit with me and we'll sing."It's better that way. I don't ruin anyone else's night by making them hear my sing."The actress revealed that the couple usually spend hours singing together.She said: "Four hours, four and a half hours. We shut the place down, it's great. He's a great singer actually. We both enjoy it."I do a lot of Prince. And recently David Bowie - 'Life On Mars' is a great karaoke song."However she admitted that rapping is not her forte, saying: "I'm just not great at it. But who doesn't love karaoke?"Olivia recently revealed she can't wait to have children with 'Saturday Night Live' funnyman Jason.She said: "[I] can't wait for children. I'm open-minded about how many, but three, which I love, is like a little party. I am not trying to have kids now - there's no strict plan for anything in my life."What happens, happens. [Jason's] so good with kids ... I've never before experienced looking at someone and thinking, 'That's who I want to raise a child with.' "