The Newsquest daily officially started the service last Monday and has already signed up almost 200 readers for its news and sport services. A morning bulletin of the Mail's best stories and an evening wrap-up of the most popular stories online with links are sent out, as well as major breaking news alerts.
WhatsApp is one of the fastest growing social media platforms, with 500 million users worldwide. Oxford Mail assistant editor Jason Collie said its advantage was the immediate knowledge alerts were definitely seen by readers.
Mr Collie said: "We're really excited at the way our readers have embraced this new platform, although we are still feeling our way with it. It takes getting your stories out there via social media to a new level because, unlike Facebook or Twitter, you know an alert has ‘pinged’ on the reader's phone demanding attention.
"During our trial Oxford United striker James Constable announced he was leaving the club. On Twitter there were six or seven tweets carrying this news, so we were relying on a reader choosing our Tweet over the other ones competing in their timeline for attention.
"With WhatsApp we knew everyone's phone pinged with our message straight away, and the likelihood was greater that it is our story they read."
Mr Collie said the key, particularly in the early stages, was not to overload the service with updates.
For news there are two round-ups a day and up to three other alerts of big breaking news or major traffic issues because the Mail did not want to 'desensitise' that alert going off on a phone, he added.
The service had also seen news tips and photographs coming back in from readers.
Mr Collie added: "To get close to 200 in a week-and-a-half exceeded our hopes and only three people have quit the service. One of those said it was because he had the paper delivered every night and so got all our stories anyway, so we're not going to discourage that.
"There is huge growth in WhatsApp. This won't replace Twitter and Facebook but you've always got to take your stories to where the market is and WhatsApp is looking likely to be somewhere our readers are.
"It is early days and it will develop but one of the best tributes was that on the first morning of the trial, someone tweeted a screen grab of the first message and said: 'The future of news delivery?'"
