As a non-muslim foreigner working in Saudi Arabia are there any
circumstances under which it would be legal for me to purchase and
consume alcohol??

Hello,

I'm afraid that the answer is a no.  Technically, foreigners resident
in Saudi Arabia are subject to the Saudi law in the same way as Saudi
citizens. Saudi law does not tolerate the consumption or distribution
of alcohol. Therefore, if you do consume alcohol in Saudi Arabia, you
are breaking local law.

The British Embassy in Saudi Arabia has published a useful guide for
Britons coming to live and work in Saudi Arabia:
http://www.ukm.org.sa/Free%20lists/LIVING%20IN%20SAUDI%20ARABIA.doc

With respect to alcohol, it says: "Sentences for alcohol offences
range from a few weeks or months imprisonment for consumption to
several years for smuggling, manufacturing or distributing alcohol. 
Lashes can also be part of the sentence; and a hefty Customs fine if
smuggled alcohol is involved.  The authorities also hand out stiff
penalties to people found in possession of equipment for making
alcohol."

It also says: "Saudis understand that the ways of non-Muslims are
different from their own and they will not generally interfere with
what foreigners do quietly, privately and discretely.  But foreigners
who take advantage of this to break the law are running serious risks.
  The Saudis are jealous of their reputation of having a well-ordered
society. They will not allow foreigners to put it at risk."

Imprisonment in Saudi Arabia is referred to as "a trying and
uncomfortable experience".

Nevertheless, according to an article by BBC News, February 8, 2001,
some alcohol can be found in Saudi Arabia.  It can be found among
foreigners who live in special quarters.  A favoured route seems to be
for alcohol to be brought into the country in diplomatic bags which
are not checked at entry.  Obviously, there is also ordinary smuggling
of alcohol as well as illicit manufacture, despite the severe
penalties.
http://news.bbc.co.uk/hi/english/world/middle_east/newsid_1160000/1160846.stm

An article in the Christian Science Monitor, May 10 2001,
http://www.csmonitor.com/durable/2001/05/10/fp7s2-csm.shtml
says "150,000 cases of spirits, most of it Scotch whisky, are smuggled
into the country every year, with resulting profits of $200 million.
Industry experts believe that 70 percent is consumed by Saudis and the
rest by expatriates... ...80 percent of the smuggled alcohol comes
from the United Arab Emirates. Another 18 percent arrives by the tiny
Persian Gulf island of Bahrain, via the causeway linking it to Saudi
Arabia."  A bottle of whisky (Johnnie Walker Black Label)  can fetch
$200. Expatriates making bootleg alcohol claim to earn $3000 per week.

This same article does mention that it is permitted to serve alcohol
on the premises of foreign embassies.  Presumably, this is because of
the universal convention that embassy premises are considered to be
under the jurisdiction of that country rather than the host country.

An article in the (UK) Daily Telegraph, February 6, 2001
http://www.corpun.com/saj00102.htm
says that the religious police do tend to turn a blind eye to illicit
drinking parties in expatriate compounds. However, the same article
also describes cases where punishment has been imposed:  The last case
of a Briton being whipped was in 1985 when he received 250 lashes. 
Since then, Western expatriates have generally been imprisoned and
then departed. A Briton sentenced to 70 lashes in 1995 was not
whipped, but instead spent 10 months in prison "fearing daily for his
life". Another Briton, sentenced to 450 lashes in 1996 spent more than
a year in prison before being deported.

Question was answered quickly and thoroughly relative to the time
period that elapsed between being asked and answered which was only a
couple of hours. Could not have expected much more from any source I
would not think and will be surprised if a commenter adds something 
entirely new that adds significant value.