In winter when I use the stationary bikes at the gym they say I am burning 450-530 calories an hour, iirc. That is with a constant cadence, so I would assume it would be about the same as riding a fixed gear. I have no idea what the numbers are for running, but like was previously mentioned it obviously depends on your intensity.

However this calorie calculator says that I'd be burning like 900 calories an hour, which I don't think is right. But it's top allowable speed is 17.5 mph.