If by "symbol" you mean to say "abbreviation" and by "element"
you are referring to the periodic table of elements, I should
preface this response by saying that there is no atomic element on
the periodic table called "oil." Therefore, it is impossible to
tell you what the abbreviated name would be (as I can say the
abbreviated name for Iron is "Fe" because it appears on the
periodic table as such).
Furthermore, "oil" can refer to a multitude of different
compounds. I feel like you are most likely referring to Petroleum,
or "fossil fuels." However, Petroleum is not an atomic element
either. Petroleum is a crude, complex mixture of naturally
occurring hydro-carbons and other organic molecular compounds.
Therefore, it cannot be represented with one "symbol" on the
periodic table, as it is not a single atom but many atoms, mostly
that of hydrogen and carbon.
However, any compound described as oil is generally a
lipid-based compound that is uniquely capable of being liquid at
room temperature (where as other lipids, like waxes and lards, are
solid at room temperature and must be melted to achieve a liquid
form). Unfortunately, there are too many different lipid compounds
of this type, which we call oils, for me to deduce which one is the
subject of inquiry here.
If by asking what the "symbol" for oil was, you meant to ask
whether there is a universal "picture" for oil, as a "skull and
crossed bones" is the universal symbol/picture for poison, then as
to what a similar symbolic picture for oil might be, I have been at
a loss to find one that is universal. Clip-art in the symbol of a
Pumpjack came up most often in my internet search for pictures of
oil. Perhaps that could be considered a consistently universal
picture, or symbol, for oil -- if you are referring to Petroleum
oil, that is.
