Difference between oil and paraffin oil

Paraffin oil is a kind of oil.
To a certain extent, oil from kitchen (like peanut oil) is similar to paraffin oil, in the use to storage of reactive metal for a short time, but may not so good for prolong period. Because oil from kitchen will decompose by oxygen or bacteria into smelly product. The purpose of using paraffin oil is to cover up the reactive metal and make it completely isolated from the surrounding (oxygen and moisture etc). As a result, the reactive metal will not form oxide or other product.
I hope this can help your understanding.

2007-11-01 09:21:12 補充：
Solid potassium reacts violently with water, and should therefore be kept under a mineral oil such as kerosene and handled with care. Unlike lithium and sodium however, potassium cannot be stored under oil indefinitely.

2007-11-01 09:21:55 補充：
If stored longer than 6 months to a year, dangerous shock-sensitive peroxides can form on the metal and under the lid of the container, which can detonate upon opening.

2007-11-01 09:22:26 補充：
It is recommended that potassium, rubidium or caesium not be stored for longer than three months unless stored in an inert (oxygen free) atmosphere, or under vacuum.

They are oil, some kind of oil.