Based on both a relatively optimistic estimate of the undrilled oil
around the world and an estimate of the total oil that has been
drilled since humans started drilling, what percentage of the world's
oil reserves have humans tapped?

80% has already gone and we are now squeezing the last few drops out
of the wells, many of which are already dry.

Of course, we can also produce oil from other resources (eg coal,
sugar) so there's no need to panic ...

Not until next year.

the West Texas basin was estimated to have 8,900 million barrels of
oil in the ground (reserves) untapped in 1998.  It is noteable though,
that almost all the early wells in Texas were "shutdown" because of
slow production in the 60-70's.

It has been estimated by many exporation executives that over 50% of
the original oil in those old wells is still in the ground.  However,
new technologies such as hydro fracturing, surfactants and
multi-directional drilling make these "dead holes" viable once again.

The new formation discovered in southern AL & off shore AL is a
significant find.  In addition to the huge reserve in alaska, Arkansas
and MS have smaller but currently producing well.  The largest problem
for the US is refineries.  A new refinery has not been brought on line
in the US ince the late 70's.

The problem is not how much, but where and price.  If price is not an
issue, the tar sands in CA have great potential for scrubbing with
surfactants.  So,  it is true... we dot not know... but I do know oil
can not be made from coal or sugar.  gasoline can, but not oil