Yeah,
the majority of our plastics do come from oil. However, plasics can be made
that are in fact bio-degradeable and don't use oil.
Oil based plasics aren't bio-degradable. The problem with non-oil based pasics
is that they cost more to make and aren't as strong
and durable as oil based ones. The History Chanel had a program awhile back on
the history of plasics and I rember that.
Maybe they found some way to improve on the non-oil based plastics so they are
tougher and don't degrade. A similar problem
of duability and strengh of a plastic happens with recycled plastics, each
latter generation of the plastic is weaker than the one before
it.