What is the order of operations on SO?

I'm curious on how the game determines who gets the orders when more orders are placed than are available at the selling price.

IE

3 people all have standing orders for 10000 each at $50 for food and 20k food hits the market at $40 and 3 batches of 5k@$42

How does the game determine who gets what? Or is it random?

Or lets say 30 oil standing orders for 5,000 barrels are filled at $22 per barrel and then 1 lucky country gets their SO filled for 371,737,318 barrels at $22 per barrel.

My experience is that the SOs are filled in order they are placed independent of the qty open on the SO. So if 50 SO's qualify for the price that the goods hit the market it will be the one that was first placed or last filled.

I believe it is _supposed_ to be a FIFO queue of sorts. If you get some goods, you move to the back of the line regardless of whether your entire order is satisfied.

But without having the benefit of seeing or knowing the code, I cannot say. I have never tested it out.