Oprah bets her chat show on an entire TV network

Winfrey launches a $400m cable channel dedicated to her brand

It began with the woman herself: Oprah Winfrey, in her finery, welcoming viewers to what she hopes will be a bright new era in broadcasting. Then it meandered through an interview with Jay-Z, a couple of reality shows, and a late-night presentation by a sex therapist.

The Oprah Winfrey Network, a TV station dedicated entirely to shows inspired by America's most powerful chat show host, went on air for the first time at noon yesterday. It is the most important channel launch for a generation, and its founder's biggest gamble in a career that spans more than 30 years. Never before has a celebrity tried to brand an entire channel in her own image. In Winfrey's case, this is a heady mixture of shows about self-help, consumerism, and advice on how to "live your best life". Never has a single TV host been able to raise the hundreds of millions of dollars needed to make it happen.

Called "OWN" by its creator, the cable channel is available in around 85 million US homes. Its stable of presenters includes the comedienne Rosie O'Donnell, the singer Shania Twain, and the actor Ryan O'Neal, who, with his daughter Tatum, will be the centre of an Osbornes-style fly-on-the-wall show. Adding to the mix designed to appeal to Winfrey's largely affluent, mostly female, fan-base is our own Duchess of York, who is to star in Finding Sarah, a six-part series in which she attempts to "heal my mind, body and spirit" following her recent tabloid sting.

On paper, this is meat and drink to fans of Winfrey, whose business interests – including a magazine, a website, and her hugely influential book club – make her the best-paid woman in entertainment, with annual earnings estimated by Forbes to be more than $300m (£190m). But the launch represents a serious leap of faith. In May, the network TV chat show that has been the engine room of Winfrey's career, will end after roughly 5,000 episodes. Its stock has fallen recently, but the show still boasts seven million viewers, down from 13 million at its peak. Winfrey is therefore gambling that a good portion of those viewers will be sufficiently loyal to change their daily routine and seek out different shows on the harder-to-find cable network.

Pundits are divided on her prospects. "How can you turn a one-hour show into a 245-hour channel?" wonders Eric Deggans, a media critic at Florida's St Petersburg Times and expert on Winfrey's oeuvre. "Even for the queen of all media, it's a big ask. The end of the chat show has to be a worry. No one knows what will happen when you cut off the thing that has always attracted people to her."

The launch has already been marked by some turmoil. Originally scheduled for 2009, it has been twice delayed. An entire management team at OWN, which is based in Los Angeles, on the other side of the US from Chicago, where Winfrey's empire has so far been built, was fired. Discovery Communications, the cable TV firm that has invested around $200m for a 50 per cent stake in the venture, was asked to commit more funding earlier this year. It agreed, but only on condition that Winfrey took a more active role in the launch.

Gauging success will be tough. No one expects the channel to turn a profit for a couple of years (which has hurt Discovery's share price) and it is hard to interpret what size of audience represents an acceptable figure. Discovery Health, the channel it replaces, gets around half a million viewers on average. OWN will easily better that, but it's unlikely to get close to the seven million who watch the chat show.

In any case, success in the cable TV game isn't just about ratings. "It's about building a brand that viewers associate with programming they like, which allows a network to charge providers more money to carry the channel," says Matt Belloni, of The Hollywood Reporter. "Will Oprah be successful? It depends on whether there is appetite for programming themed around her brand." Winfrey was somewhat more bullish last week. "This network is going to work," she told an interviewer. Asked why, she gave a short but effective response: "I know what people want."