"Your view of economic [sic] is badly hampered by an assumption that the global oil market is as 'free' as the American laissez faire ideal so vociferously worshipped on these pages."

I don't assume the oil market is 'free'.

"If the hypothetical post-liberation Iraqi oil ministry unilaterally tripled their price (or even merely doubled it), do you think they would sell any on the open market?"

Of course not, but that's what Mary Anne said.

"Would the US buy from them, whether or not from a collective sense of guilt, if the profits were guaranteed to be used to rebuild Iraq... or would American (and multinational) oil companies continue to 'buy low, sell as high as possible'?"

Everyone "sells as high as possible". Everyone likes to buy at a lower price. Oil companies aren't buying and selling, this it's mostly done in the oil future market. Just as a national money (such as the US dollar) are bought and sold in the future markets.

"What do you suppose would happen to Iraq's standing in OPEC (which, you seem to have misplaced, is where the real price-fixing occurs)?"

"Real price-fixing occurs" by agreeing on limiting oil supply/production.
Btw, there isn't anything really "wrong" with OPEC trying to stablize prices by controlling oil supply (limiting oil production). It would good if the Arab countries gain steady wealth, and also use that wealth to invest in infrastructure & education/healtcare which would allow these countries to generate wealth other than by selling oil.
For example with Iraq I think some of the oil revenues should go into increasing the farming capability of the country (I would include forest projects as farming- I think if you do things which reduce dust storms that would be a good thing.).