My first AGA cooker (bought in 1996) was an Oil fired one, it was an reconditioned original standard AGA with a Don's conversion kit. It worked fine until we had it serviced! After that it seemed to be forever going wrong as the burner kept coking up, the flame burnt yellow and the AGA went cold. Also it was forever loosing heat when we wanted it to be hot such as at Christmas. When we moved out the new owners ripped it out along with the bespoke kitchen!
I have since learnt that the coking and going cold appears to be a common problem with oil fired AGA cookers. I think it's more so with oil conversions but I have also read that purpose built oil AGAs get the same problems. I have been told it's because the quality of kerosene in this country is of a low standard. I do know that you can pay a higher price and get a better quality fuel but I still think you are going to get the problems associated with an oil AGA, and you are still going to have to get them serviced twice a year. They will also cost you about £25 a week to run. I do know that one of the ways around this is to fit a oil fired pressure jet conversion to the AGA which means a service of once a year, see the link for the other benefits. AGA Rayburn don't approve of these conversions apparently. The other way is to buy a 30 Amp AGA (which I have and it's great) or get a wood fired Esse which is alot cheaper and 'green'. You can get an add on electric module for the Esse so then you will have the best of both worlds.Google+