[BroJoeK]

Sherman Logan: "The Confederate government never officially put an embargo into effect.
It was a purely voluntary effort by southerners, though the force of public opinion made compliance with it almost universal."

Right, the Confederate government did not need to enforce the embargo, but certainly did not oppose it, making the embargo effectively national policy.
Here's what I'm looking at:

• According to this site, in 1860 the South exported 5 million bales of cotton worth $200 million.

• Recent studies show that world-wide demand for cotton remained high during the four years of 1861 to 1864, meaning the potential was there for Confederates to export in four years another 20 million bales worth $800 million.

• That was certainly enough to finance the war, supply every Confederate soldier with a Sharps-type repeating rifle (@$60 each versus $20 for Springfield-type muskets) and purchase a large modern navy to defend its exports.

In short, second only to the foolishness of firing on Fort Sumter, the Confederacy's decision in early 1861 to embargo cotton exports can be said to have cost them the war.

Sherman Logan: "Most of the effect of the embargo was lost because of the immense cotton exports of previous years, which meant European warehouses were bulging with cotton."

Yes, but according to this site:

"Previous researchers have asserted that the South faced stagnating or falling demand for its cotton.
Surdam's more complete model of the world market for cotton, combined with additional data, shows that the reduction in the supply of American-grown cotton induced by the Civil War distorts previous estimates of the state of demand for cotton.

"In the absence of the drastic disruption in the supply of American-grown cotton, the world demand for such cotton would have remained strong."

[Sherman Logan]

In short, second only to the foolishness of firing on Fort Sumter, the Confederacy's decision in early 1861 to embargo cotton exports can be said to have cost them the war.

I am very unclear on why they thought it would work. While embargoes prior to the Revolution, an early form of what we today call economic sanctions, may have had some positive effect, later attempts to implement the policy under Jefferson and Madison were wildly counter-productive.

I guess they just got to believing their own propaganda about King Cotton.