How a microwave seems to heat oil just as well as water

[Zeno Marx]

I always understood that a microwave oven heated things by the microwaves (wavelength about 10cm) vibrating the polar water molecules so they try to line up with the flipping electromagnetic field and they then impart their agitation to the surrounding matter of the food. Now if this story checks out things with less water should heat slower in microwaves. I was giving this explanation to some friends of mine and as an experiment put a bowl of vegetable oil in our microwave, something that if only the water was involved you would expect to heat slower, yet it seemed to heat just as fast as anything else (in fact faster than a bowl of just water would - I know there are some specific heat issues here). what is going on here? Is the story we have been told about how microwave ovens work not the whole truth?

 

[mfb]

Many things absorb microwaves. Water absorbs them very well, but other chemicals absorb them as well.
The lower specific heat is an important factor, too.

If you want a fair comparison, you have to put both materials in at the same time, otherwise most of the microwave energy will get absorbed in the target material in both cases.