1.  How many gallons of gasoline are produced from one barrel of oil?

2.  Given the US uses about 21 million barrels of oil daily and the
average driver gets 20 MPG.  How much oil would be saved by increasing
the MPG by one(1)?  I've read that by increasing our national average
to 30 MPG we could become independant of foreign oil.

The US produces about 7.6 million barrels of oil per day.  
http://www.cia.gov/cia/publications/factbook/geos/us.html

To completely illeminate its dependance on foreign oil, it would have
to decrease its oil consumption by about 66%.  That is completely
unrealistic in any short term plan.  And in any long term plan, you
must also consider that the US production of oil is probably on a
continuing downward slope in the future.  The fact is that the US will
be dependant on foreign oil for a long time.

Only 45% of US oil consumption is by autos.
http://www.terrainmagazine.org/article.php?id=13323
This is a total of about 9 million barrels per day.  Notice that this
is less than half of total US oil consumption.  Even if everyone in
the US stopped driving, the US would still have to import oil for all
its other uses.

Question 1) 1 barrel = 42 gallons

Question 2) 20 mpg uses 9 million barrels per day... so 
21 mpg would use 8.6 million barrels per day.
30 mpg would use 6 million barrels per day.

The statement you mentioned "by increasing our national average
to 30 MPG we could become independant of foreign oil" might have been
in reference to cars only... notice that US autos could run soley on
US oil if they averaged 30 mpg, but that is unrealistic in the sense
that US oil will always go part to cars and part to industy/homes.

Of 42 gallons of petroleum the amount of Gasoline varies quite a bit.

Refineries are tuned to make more of some products then others
depending of the time of year, market prices, Technology available,
air pollution regulations, and the kind of oil it is.

Kerosene, gas, Fuel oil, and road tar all come out of that barrel as
well as energy to run the mill and pump the products.