torchwood.tv

I have found many fan sites claiming that Russel T Davies announced in a recent interview for Children of Earth that they are considering ideas for series 4, however, this depends on the response from Children of Earth (and 5.9m viewers makes it look hopeful). However, whether these sites are reliable is unknown and there has been no announcement from the BBC concerning a 4th series currently. From the ending of Children of Earth it dosn't look too hopeful but there are possibilities in the story to continue for another series. The response from the UK is very optimistic for the chances of another series, and once it has aired in America, it is likely there will be a very positive response from them too.
We just have to wait and hope for a press release from the BBC confirming rumours of a 4th series, but its looking fairly optimistic at the moment