Industries with their own rollingstock

[dave1905]

So where does the industry keep the empties?

The industry would have to build storage tracks for its cars or lease storage from the railroad or another industry. Private cars on private track are not subject to car hire or demurrage.

And when a customer of the industry orders a load, I guess as long as the industries own cars are available, they would use those for shipping the load?

And the company would pay the railroad a switching charge to move the car from the storage track to the industry.

What if all the industry's cars were in use? Where would the needed empties come from?

If the cars were general service cars or general service cars could be used they would order empties from the rairroad just like any other industry. It is pretty unlikely that the cars would be general service cars. So if the industry ships tank cars and it runs out of empties to load, it doesn't load any cars. At many chemical and auto parts plants the empty cars are often "hotter" than the loaded cars. Teh plant will track where the empties are more closely than the loads.

Would the indutry's cars typically be in captive service?

Private cars and that's what they would be, are captive in that the car owner determines where they are loaded and where they go. So the empty private cars would always go back to wherever the company has said to send them. Now if they send 100 tanks each to plants A and B and it turns out that plant B needs 125 cars, the industry can have the railroad move 25 cars from A over to B, but they will be "revenue empties" and considered a "load" because the railroad will get paid and the cars will have a revenue waybill on it.