Question
If you could I need some help to explain why you don't use oil driven pumps in pond features. I have a colleague that does not seem to understand the difference, and I think this would help a lot of other folks as well.

Answer
Dear Steve,

When you can assure that no oil will get in to the pond there should be no problem.
However as the risk is always available and we do not want the risk of fish dying, when mostly chose for oil free pumps.
This takes away the risk.
However some other pondkeepers keep on using them, as long as they don't leak they will tend to promote it as it is somewhat cheaper.
Now there tend to be more and more A new type of pump available in the pond world and this is airlift.
Hope this helps.

Regards,
Raf